@BingBang:
At 12:37 it seems like both of their attacks make contact. It’s hard to tell but why else would the ground get destroyed by Katakuris attack. They both fall down exhausted. It’s been established that 10 mins is all luffy needs to recover enough stamina to at least move and use haki again. That’s why it goes back to them at 12:47. Luffy couldn’t continue and neither could Katakuri. They spoke and Katakuris endurance finally gave way. It was a draw folks.
Luffy may be in his last legs, but he's the only one of the two who can use them to leave the battlefield. He's ended more obviously victorious fights in similar or worse condition (Lucci, Moria, Doflamingo) and no one's argued about it, so I don't see why this one's any different.
It may have been by the slimmest of margins, but this was an unambiguous win for Luffy.
–- Update From New Post Merge ---
This actually reminds me of the Jackie Chun vs Goku fight in Dragon Ball. The two got each other in one last mutual hit, knocked themselves out, and neither got up before the ten count ended. From there the victor was decided by whoever got up first and could declare themselves the winner. Goku tried and failed. Jackie Chun succeeded. Jackie Chun was the winner.
Not a tournament scenario, but this situation isn't otherwise that far removed from it.