It's not the first time you'll hear this argument, and it certainly won't be the last, but Sydney FC's tremendous exploits in the A-League this season will again bring Australia's finals system into sharp focus.

In Australia, you cannot be considered the champion, the country's best, unless you win the big one. The grand final. Your competition's showpiece event.

Now the A-League season comes down to this: one match in which premiers Sydney FC face off against runners-up Melbourne Victory in a heated decider.

And if Sydney FC fluffs its lines at the worst possible time, it will be the biggest showcase of how unjust the finals system is in Australian football's history.

Never before has the A-League had a team so superior to the rest in the regular season. Sydney FC broke a bunch of records en route to lifting the Premiers' Plate — with 66 points from 27 games, it amassed a record points tally, and also broke the record for biggest margin between first and second, sitting 17 points ahead of the Victory.

That dominance came in no small part due to the sensational exploits of Milos Ninkovic, the clear winner of the Johnny Warren Medal, finishing seven votes ahead of his nearest challenger.

Despite all that, Sydney FC must prepare for what essentially boils down to a coin-toss gamble, taking on its oldest rival in the heat of a grand final, to only now be declared Australia's champion.

Possibly on a quagmire pitch too, while we're at it.

Milos Ninkovic (right) was head and shoulders above the competition in terms of individual performances. ( AAP: Paul Miller )

In the here and now, we can all privately acknowledge Sydney FC is the best in the land, prior to the grand final.

Follow the A-League grand final live You can tune in to ABC Grandstand's live coverage of the A-League grand final between Sydney FC live.

You can tune in to ABC Grandstand's live coverage of the A-League grand final between Sydney FC live. It will be broadcast nationally on ABC News Radio, and live on ABC Digital EXTRA, from 4:00pm AEST Sunday.

It will be broadcast nationally on ABC News Radio, and live on ABC Digital EXTRA, from 4:00pm AEST Sunday. You can also stream it online and via the ABC Radio phone app.

You can also stream it online and via the ABC Radio phone app. ABC News Online Sport will bring you all the action in our live grand final blog.

But should Victory pull the rug from under their feet — and they're more than capable of doing it — history won't be kind to the Sky Blues' legacy.

There won't be a giant asterisk next to Melbourne Victory's inscribed name on the trophy, saying they won five fewer matches and endured seven more losses than Sydney.

All we'll remember is that Melbourne Victory won the 2016-17 A-League grand final. And it won't even tell half the story.

Isn't this just pre-emptive excuse-making?

Yes and no. In Australia, you have to prove yourself in one final crunch decider to rubber stamp your greatness.

The great teams of A-League history all did it — both the Melbourne Victory and Brisbane Roar can boast two teams in this category — and now Sydney FC must run a similar gauntlet.

Finals boosters may argue what matters at the end is the big glittering trophy, and not what came before.

No-one cares about the group stages in the World Cup, only who wins the final right at the end, right?

Sydney FC was imperious throughout the regular season, but has to put that all on the line to be considered 'champions'. ( AAP: Dean Lewins )

Except, that's not 100 per cent true. Take the recent Euro tournament, where Portugal snuck in to win its first major title at France's expense.

Les Bleus were widely thought to be the competition's best team, while Portugal muddled its way through the group stages, drawing all three of its matches against the heavyweights of Austria, Hungary and Iceland.

Portugal's win proved joyous to the Portuguese and Cristiano Ronaldo's legions of followers, but to everyone else, it left something of an empty feeling. A slightly sour taste of daylight robbery, or at least annoyance at France's choke when it mattered.

Are we really so willing to put a team's legitimate claims to greatness at risk for the sake of some TV dosh at season's end?

We can't compare the group stages, or even the entirety of a major cup tournament, to the regular season of a league competition. In cups, shocks happen. It's why we watch them in the first place.

But the comparison discounts the A-League's 27-game marathon before April in order to elevate the importance of a handful of finals matches.

Sydney should walk this, if history has its way

This is of course all purely hypothetical. If history plays out on Sunday evening, Sydney FC should get over the line and claim its rightful spot as A-League premier and champion.

Indeed, of the 12 A-League seasons prior, seven of those have witnessed "double" winners of both premiership and championship.

Of those seven teams (the Victory three times, the Roar twice and Sydney FC and Adelaide once), the Victory (12 points in 06-07) and the Roar (eight points in 10-11 and 10 points in 13-14) saw their tremendous premiership dominance translate into a championship.

Such leads would have seen similar pressure placed on those two teams to win the match that mattered and ensure all their hard work in the regular season wasn't for nought.

For those that didn't follow up topping the table with a grand final win, the argument could be made for the seasons being a tight one, that it really was anyone's game heading into the decider, and that none of the premiers led by more than three points at regular season's end.

Except in the case of Adelaide United, in the A-League's inaugural season, where they finished seven points ahead of Sydney FC, a margin surely emphatic enough to suggest the Reds were Australia's best.

Only the history book begs to differ. Sydney FC was crowned the inaugural champion. Thanks to the bear trap that was the Page play-off system, the Sky Blues dumped Adelaide United into a preliminary final, before the Mariners eliminated Adelaide.

Adelaide's Premiers' Plate backers might be forgiven at this point for hoping some sort of karma lays waste to Sydney's chances on Sunday.

What about those who want the underdogs to prosper?

Why is a Sydney FC win important for the competition? Because recognition of how good this team was will add cache and credence to the A-League's heritage, knowing we can look back at the honour roll, point to 2016-17, and say "that was a great team".

But Victory fans, assuming they're not so angry to have stopped reading by now, will of course not give a toss about Sydney FC's salty tears if the favourites fall short. Neither will Western Sydney Wanderers fans, for that matter.

Melbourne Victory, in a one-off match, are more than capable of edging Sydney FC in the decider. ( AAP: Joe Castro )

Australians love an underdog, so we're told. Remember Leicester City? Everyone loved them and their plucky antics, showing up the big boys in England to win a Premier League title no-one saw coming.

In the scramble to pump out content about the team everyone wanted to know about, Australian media would scratch its head trying to find a comparable story to Leicester from Down Under.

The truth is, there were none to be found. Not one without several caveats, anyway.

The finals system, and the resultant disregard for the regular season, means any shock wins in the decider could be put down to mediocrity peaking at the right time, as much as good fortune or genuine pluck.

Leicester's story was incredible because they won the marathon, not a one-off 100m sprint where the Usain Bolt-type tripped over his feet.

The regular season presents the true test of any team, where the cream ultimately rises to the top.

As far as underdogs go, Melbourne Victory aren't exactly the perfect example. A well-established team with plenty of domestic history and some serious players, they're in the grand final by virtue of being second-best to Sydney FC. Very second-best. Seventeen points behind, seven more losses and five wins fewer second-best.

And yet they've got more than a puncher's chance of being considered champions at Sydney's expense.