You know, I'm absolutely sure that had Kubo written that fight and not Oda, you'd all be on my side. Think back to the CP9 arc. Blueno could barely take Gear 2 punches from PRE-timeskip Luffy, and he was certainly no wimp. Now, I really think Oda shouldn't have included the punch-catching scene. I'd accept that the difference between "strongest swordsman at Fishman Island" and "someone trained by the strongest in the world" could be that wide. After all, the SECOND-strongest at FI was only high East Blue-level. But with the punch-catching scene, there's just no excuse.
To me, there's two BIG Sea Kings in the living room if Oda wants us to believe the Paradise-New World difficulty jump is as big as he seems to be implying it is. The first is CP9, particularly Lucci. I use Lucci as a measuring stick to determine how strong other characters are for two reasons: first, he's the strongest character we actually have a concrete figure for, and second, his former position implies (to me, at least) certain things about how strong he is in relation to other characters. After all, there's only one CP9 in the world, and Lucci is the strongest member. That could conceivably mean he could be sent on assignments in the New World. If so, there's not much use in an assassin who can be punk'd by the average Joes over there, so it's quite likely Lucci is stronger than an average New World captain, if not by much. And Luffy beat him. Therefore, Luffy may ALREADY have been New World-ready at Enies Lobby. Though, this is just me making assumptions again.
The second and more obvious Sea King is Kid. We're told he's made it big in the New World, even inconveniencing the Emperors. Thing is, he went there right from Sabaody, at which he didn't seem all that much stronger than Luffy. If we're to accept that Kid was New World-ready back then but Luffy wasn't... I'm not sure what that means.
Sorry for continuing this argument, by the way, I just really, REALLY love debating!