Zoro didn't get humiliated in Sabaody though. He was already down and out before Kizaru even showed up. Kizaru just made him his first target.
Some Zoro fans were going as far as to act like they had some kind of fight, and Zoro lost, just to push the agenda.
It was always Luffys fight to be had because he had to watch, powerless, as his entire crew was wiped out before his very eyes, as a byproduct of Kizaru showing up.
Luffy trained for two years so he could prevent something like that from happening ever again. Now here we are, with practically the same exact scenario of Sabaody, just on a grander scale. Of course it was going to be Luffy preventing history from repeating itself, because that was the backbone of Luffy deciding to split the crew apart for two years, so they could get stronger, and he'd be able to protect his crew no matter what.