The Diamondbacks have capitalized on the Giants’ offensive ineptitude and slew of injuries, winning eight of their last 11 games and taking a two-and-a-half game lead in the National League West. A year after losing 97 games, the team is primed for a playoff push. Arizona hasn’t missed a beat, despite issues that might have taken down a lesser team. Losing Stephen Drew and lacking an everyday first baseman might push other teams out of the race, but the Diamondbacks are playing some of their best baseball right now.

Their success is a testament to an improved bullpen, potent offense and a young, effective starting rotation. But the rotation would be even more potent these days had the team not made a questionable trade last season — a trade that seems even stranger by the month and is still without reasonable justification. It’s a trade that — if avoided and all else were held constant — would likely have the D-backs with a firm handle on a playoff berth. It’s a trade that sent one of the best starters in baseball, Dan Haren, to the Angels for Joe Saunders, Tyler Skaggs, Rafael Rodriguez and Pat Corbin.

The trade looked bad at the time, but now looks even worse given how quickly Arizona has improved. Teams don’t tend to deal much for one and a half years of a starter — as evidenced by the returns on Cliff Lee and Zack Greinke — but Haren was signed to a team-friendly contract and had $25.5 million remaining through 2012 when the trade went down. His contract also had an affordable-given-how-great-he-is option for $15.5 million in 2013, with a buyout of $3.5 million. That was worth a great deal.

What makes the trade look even worse is that the team already had a good deal of money coming off the books. Brandon Webb‘s contract had expired. Chris Snyder, Chad Qualls and Conor Jackson were traded. Edwin Jackson brought Daniel Hudson. Adam LaRoche’s option was declined. And Bobby Howry wasn’t brought back. With the Haren trade, the team was seeking salary relief but it wound up dealing off one of its most valuable assets for 60 cents on the dollar.

An ace with three and a half years left on a team-friendly contract is worth a lot more than a fourth starter, two high-risk prospects pitching in the low minors, and a reliever who can’t strike anyone out. Skaggs and Corbin have looked good in the minors so far, but by the time they’re ready to make an impact in the majors, the Diamondbacks might be in a different position.

Which brings us to the present, where the team seems caught in a troubling zone of being a contender without acting like one: hoping that Willie Bloomquist could hold down the fort at shortstop and that Jason Marquis could shore up the back end of the rotation, are but two examples. The bullpen already was solid this season, but the team decided to trade Brandon Allen in exchange for Brad Ziegler.

Some of these decisions could have been avoided had the team better assessed where it was headed and held onto Haren for at least another season. The Diamondbacks have a solid group of young players and modest payroll commitments into the future. But it sure seems like five years from now we’ll acknowledge the Haren trade as one of the biggest baseball-management mistakes of the decade. That the deal came with an interim general manager only makes it stranger.

Sure, Arizona might win its division this year — and it could certainly succeed in the postseason with a Kennedy-Hudson-fronted rotation — but boy would the Diamondbacks have been scary with Haren as the ace of that group.