Nah, you should reread the fight- it’s really good, for one thing. There’s constant focus on how perfectly matched the two are, that’s why the fight starts with a chapter called 互角, which means equal/stalemate. The idea that Sanji only got beaten up cause Mr 2 transformed into Nami is overstated and ignores a lot of the fight- including the fact that Mr 2 tries a couple of tricks before turning into Nami that he thinks would disarm Sanji and… fails miserably and allows Sanji to land a few free hits on him in return.
But it’s full of imagery showing the two as equals, attacks matching each other, “he countered my x attack!”, constantly mirroring the two opponents, taking damage at the same time.
That’s an extreme diff fight in my book. One of the rare ones in One Piece where it’s not a Strawhat overcoming an opponent, but two evenly matched guys going at each other with all they have.
I think the extreme difficulty fights are mostly Luffy's cup of tea, as usually those are the final obstacles and Luffy isn't really needed for anything else and the rest of the crew tends to handle the aftermath.
Luffy always gets the hardest fights that need days to recover, but I still think the others get fights that are as difficult in their own way. The difference between extreme-extreme diff fights and low/mid-extreme diff fights if you want to get slightly ridiculous about it.