Serge Ibaka has changed the entire look and feel of the Western Conference finals. A non-fan watching from the future would assume Games 3 and 4 came from a different season than Games 1 and 2 — that the team in black jerseys won the first series, and the blue team then signed some monstrous destroyer who helped them flip the result a year or two later.

Ibaka’s importance was predictable; there’s a reason my whole series preview was about his injury and his role in Oklahoma City’s ownership of this matchup over the last three seasons. On a podcast after Game 2, ESPN.com’s Kevin Arnovitz and I bristled at the two absolutes flying across the airwaves:

1. The Spurs were only winning because Ibaka was out.

2. The Spurs were playing so well that Ibaka’s presence couldn’t possibly tip the balance.

Anyone proclaiming a counterfactual outcome with certainty is usually selling you garbage. It would seem ridiculous that a player averaging 15 points per game could swing a series in which the Spurs won Games 1 and 2 by a combined 52 points.

Basketball is funny that way. It’s complicated. Ibaka might be an unspectacular scorer, but he’s a spectacular defender, and he can affect every single defensive possession. He can’t do that on offense; he doesn’t get the ball enough, and there’s only so much impact a solid midrange shooter can have with minimal touches.

Opponents feel Ibaka’s presence on every offensive trip. Even away from the ball, he’s an unseen horror movie villain, lurking there somewhere, spooking dudes as they get ready to creep around the corner into the unknown. In Games 1 and 2, Tim Duncan was driving right through Kendrick Perkins, Nick Collison, and Steven Adams for layups. Even Tiago Splitter drove the ball all the way from the elbow against Collison in Game 2 and laid it up in his grill, and that’s saying something, because it seems at times like Splitter is the tallest player in history who can’t dunk.

But with Ibaka around, Duncan is taking shots like this:

The play starts with Perkins leaping out to contain a Manu Ginobili–Duncan pick-and-roll nearly 30 feet from the basket, a dumb thing Perkins does because he thinks he’s fast, and because the Thunder believe in the energizing effect of enabling aggression across the full roster. They go haywire sometimes, as Perkins does here, but Ibaka amounts to an in-possession reset button that cleans up all messes.

Here, Ibaka abandons Boris Diaw in the right corner for no real reason, as Kevin Durant and Adams have this Kawhi Leonard–Duncan pick-and-roll contained on their own:

But that is who the Thunder are defensively — an ultra-springy team that leverages its athleticism to create chaos. Ibaka’s mad scramble amounts to a wager: We’re going to run around like insane people, and that’s going to create openings, but we’re athletic enough to close those openings before you can take advantage. Want to make that pass across the court to Diaw? Have at it. We’re ready to run.

That system falls apart without Ibaka. That’s why it was silly to claim that the Thunder could not possibly have slowed the Spurs machine of Games 1 and 2 even with Ibaka around. They are an entirely different team when he plays.

And he has played well enough to reignite an old debate throughout the past week: Perhaps the Thunder made the right call in choosing Ibaka over James Harden.

Here is where a portion of readers roll their eyes. We’re going down this rabbit hole again? Can’t we let the Harden trade die?

No, we can’t. The Harden trade will go down as one of the 10 or so most fascinating trades in league history. It’s endless, with dozens of intertwining narratives — money, pride, misdiagnosis of talent, opportunity, the ethics of sacrifice, and more. And on a very basic level, 23-year-olds as good as Harden just don’t get traded. If stars get traded, it’s usually in their late twenties, and often when they are even older, when teams must at least think about how their game might age. That is the nature of the NBA’s player contract timetable.

In a literal sense, the Thunder made a choice: Ibaka and Harden came into the league the same year, meaning their contracts worked on the same schedule, and Oklahoma City re-signed only one of them. It was worried it could not afford all four stars without triggering heinous luxury-tax bills that might injure Clay Bennett’s rapacious energy empire.

Harden is an offense-oriented player who needs the ball, and the Thunder already had two of those in Russell Westbrook and Durant. Harden’s skills were at least somewhat redundant, even though the team gradually found ways for all three to play off of each other. Ibaka is a defense-oriented rim protector, and the Thunder had no one like him.

And so they chose, the story went. In reporting on the Harden trade nearly two years ago, I estimated that a minority of NBA executives with whom I spoke — maybe 20 percent — thought the Thunder had chosen incorrectly. They also framed it as an either-or choice.

But that simplifies a narrative that has only grown more complex over time. Did the Thunder have to choose at all?

The evidence is all over the place. The Thunder spent much of the summer of 2012 conducting stealth Harden trade talks, searching out potential impact players on rookie contracts — Anthony Davis, Bradley Beal, Klay Thompson, Jonas Valanciunas, and others. They made at least one formal extension offer at well below Harden’s max — a four-year, $52 million deal, per Yahoo’s Adrian Wojnarowski. There may have been other, lower offers earlier in the process.

Those actions don’t suggest that the team was super-serious about keeping him. But with less than a week to go before the October 31 extension deadline, the Thunder stepped up with a new offer: four years, about $55.5 million — only about $4.5 million less than Harden is earning over the first four seasons of his max deal with Houston. By all accounts, that was a real offer, not a face-saving gesture. The Thunder wanted Harden to take it.

The Thunder at that moment had chosen to keep both Harden and Ibaka. If they were willing to go so close to Harden’s maximum, it’s borderline irrational they wouldn’t go the whole distance. Is $1.1 million per season really worth sending away a star for Kevin Martin and three unknown assets?

That $1.1 million matters, and the finances surrounding this deal are still evolving — and will keep evolving going forward. That small savings could determine whether the Thunder pay the tax in one season, help them avoid skyrocketing into a pricier tax bracket, and enable them to use more of the midlevel exception at some point.

But $1.1 million … yeesh. And here’s the amazing thing: The cap and tax levels have jumped so fast since the Harden deal that now it appears the Thunder could have re-signed Harden at the max and potentially paid the tax in just one season — the current 2013-14 campaign.

Ducking the tax would have required the use of the amnesty provision on Perkins, and there is no realistic scenario in which they could have come in under the tax line this season. So there’s the breakdown:

• 2012-13: The final year of Harden’s rookie contract, and thus no tax concerns.

• 2013-14: Tax time. The Thunder could have limited the tax bill had they amnestied Perkins, replaced him with a $2 million guy via a piece of the midlevel, and given their 13th roster spot to a minimum-salaried player. And to be clear, all projections going forward in these scenarios do not include anyone the Thunder received in the actual Harden deal.

That may not be a realistic scenario. Perhaps the Thunder would have paid more for a Perk replacement and used another salary slot to carry a 14th player. And remember: Teams still have to pay salary to the guys they amnesty. There was no way to duck the tax this season, and the cap/tax payroll at minimum would have come in at about $85 million — nearly $15 million more than OKC is paying in real life.

• 2014-15: This is where it gets interesting. The league is projecting the tax line to jump more than $5 million next season, all the way up to $77 million, according to a memo first unearthed by Larry Coon and since verified here. Give Harden the max and erase Perkins via amnesty, and the Thunder would have about $69.5 million committed to nine players, including their 2014 first-round pick. (And we’re even giving that guy 120 percent of the rookie scale, which is generous, since the Thunder cheaped out on Andre Roberson, giving him the minimum 80 percent.)

That gives us about $6.5 million to fill at least four roster spots, and the Thunder would probably want to leave themselves a little breathing room. But that’s enough to use a decent chunk of the midlevel on one or two guys, add at least one minimum player, and stay under the tax.

Remember: We’ve still got to pay good ol’ Perk. So the bill for this team is coming in at about $86 million, probably about $12 million more than the Thunder will actually pay next season. But we’ve ducked the tax!

• 2015-16: We’re getting into uncertain territory, but with Harden at the max, the Thunder would have about $65 million committed just to their four stars. Good news: Adding four rookie contracts (Perry Jones, Roberson, and two picks) gets you to about $71.5 million. The league projects the tax line at a whopping $81 million for that season, so we’ve still got some room to play around, assuming the Thunder had packed the 2014-15 roster with only one-year contracts.

But things are getting tight, and this would be the first year of Reggie Jackson’s new contract. The Thunder wouldn’t really need Jackson in this scenario, and the tax line could jump further between now and 2016 if league revenue beats projections. There is no Perkins amnesty payout to worry about in this season, either.

Bottom line: It’s very possible the Thunder dealt Harden in fear of a luxury tax they might have paid in just one season had they kept him at the max. They would still have spent at least $30 million or so extra in payroll over this full four-year span, including one tax season, but that’s chump change considering the insane valuation of NBA franchises. The Bucks just sold for $550 million, and Hank Scorpio can’t even get into the Clippers’ bidding process.

It is insane to think the Thunder chickened out on paying one of the league’s 15 best players over one measly tax season, especially when they came within $4.5 million of offering him a max contract.

But there are caveats:

1. Oklahoma City had no way to know the cap and tax would jump this fast — about $5 million per season over the next two years, and perhaps even more going forward. Everyone knew the levels would keep rising, especially with a new national TV deal coming in 2017, but the speed of the increases has surprised most teams.

2. The cap did not jump at all between last season and this season, which is odd, considering how much it is going to leap soon. The Thunder in dealing with Harden nearly two years ago may have expected an earlier jump. Max salaries are determined as a percentage of the cap level in the first year of the contract, and so the flatlining of the cap artificially depressed Harden’s contract.

The Thunder might not have expected that, and had they anticipated a quicker jump, their projections at the moment of truth would have looked scarier.

3. These fake rosters with Harden are thin. Oklahoma City turned Harden into three key pieces going forward: Adams, Jeremy Lamb, and a pick coming from Dallas in this draft — the no. 21 pick. Adams and Lamb have played key roles against the Spurs, and Adams especially looks like a crucial building block. There was a chance the Mavs pick would have become unprotected down the line, but the Thunder get a shot at a cheap player in a deep draft.

The retort: How deep do you really need to be with three of the league’s 15 best players and a perennial Defensive Player of the Year candidate? The Heat are starting Rashard Lewis now, and they’re about to make the Finals. (Also: They play in the East.)

4. Unlike most small-market teams, the Thunder are paying into the league’s new revenue-sharing system instead of receiving money. They paid about $4 million into the system last season, per several sources around the league, while bigger-market teams such as Atlanta and Washington received cash. The Bobcats got $20 million, and the Grizzlies about $15 million. Every buck matters.

5. After the lockout, the league retroactively kicked up the value of Durant’s max contract, costing the Thunder about $3 million extra per season — about $15 million total. The Thunder protested, and last summer, league owners voted to repay the Thunder a portion of that $15 milion. So the Thunder are getting a extra few million they didn’t expect at the time of the Harden trade, which could have offset some of the tax and amnesty payments.

6. The Thunder may have thought Harden wasn’t quite this good, since he racked up All-Star-level per-minute numbers in part against bench players. Their GM, Sam Presti, came to Oklahoma City from San Antonio, a franchise that prizes the idea of players sacrificing money for the greater good.

Harden might just not have fit the team’s cultural vision. And if the Thunder did misevaluate Harden’s talent, they were not alone. The league as a whole underestimated him.

7. The Thunder under Presti prize flexibility. Keeping Harden would have hamstrung them a bit, even had they managed to avoid the tax in all but the 2013-14 season. Paying that one year could have forced the Thunder into some extreme tax-avoidance gymnastics, since they would fight like hell to escape the extra-harsh penalties that come with repeat tax payments.

Butting up against the tax takes certain team-building bullets out of the chamber. You don’t get to use the full midlevel exception or biannual exception, or participate in some sign-and-trade transactions. Taking on extra money in trades becomes impossible. Filling out the end of the roster would have been an adventure.

If one of the four stars suffered some permanently damaging injury, the Thunder would have been stuck without options. Durant will be due a monstrous new contract in 2017, and it’s possible the Thunder would have had to make some sort of cost-cutting move to fit the next batch of star deals. Harden might have carried more trade value at age 23, as an impending restricted free agent, than he will halfway into a max deal that ends in his unrestricted free agency.

And so the Thunder have three stars and lots more young pieces instead of four stars and a comparably bare cupboard. They’re in the Western Conference finals either way. But let’s not act as if they clearly chose one guy over the other, or, on the flip side, as if keeping both would have doomed them automatically to unbearable tax hell.

One Other Conference Finals Note:

Don’t be surprised if the Spurs try Leonard on Westbrook tonight, shifting Danny Green onto Durant and Tony Parker onto Jackson. Westbrook is just physically overwhelming Parker, and Green isn’t quite quick enough for the Westbrook job. Leonard slides a bit faster than Green, and he’s longer and stronger — good for cutting off Westbrook drives.

It’s not ideal, since Leonard is the team’s best option on Durant. And there’s a certain logic in tempting Westbrook to shoot a lot, since he might shoot Oklahoma City out of productive possessions. But Parker can’t handle him, and Durant is going to score regardless. The Spurs have already had some success using Ginobili on Westbrook, and guarding Westbrook with a wing player allows them to switch the Westbrook/Durant pick-and-roll — a play that really hurt them in Game 4, with Westbrook finding Durant on a bunch of nice passes he normally has trouble making.

I suspect the Spurs might try this before going smaller, with Leonard at power forward, the adjustment a lot of folks are suggesting. They might do both, but the Spurs view Diaw as something of a hybrid forward, and their system on both ends is based in part on the presence of two big men with wide skill sets.

Enjoy Game 5. What an NBA moment.