It was obviously a joke, but the fact that he chose to say "stronger than even Kaido," singling out Kaido of all characters, during the same period that Kaido was revealed as the "World's Strongest Creature" speaks volumes.
I think OP is often guilty of focusing on current events (just like every other manga) and tries to construct a framework for the current band of characters, often with exaggarations, especially when it comes to villains
Kaido (and BM) are the focus of the current big storyline, there are plenty out there that are ''left out'' and (again, as in most manga) they are not thrown in when making comparisons; Akainu, Kong and Shanks come to mind, so does Dragon, maybe the Gorosei, obv BB after these years
yes ofc it can be argued this way or that and I agree that you would win atm, but because I think Oda does not have the powerscale all worked out, yet still very well balanced in the actual tiers themselves (as we have seen in the past), I do believe what my thoughts on this will eventually happen
which isn't to say that Kaido isn't a top dog, I just think that the few characters at the top of OPverse are all able to stand against achother and the tiniest of things (be it events during the course of teh fight, motives for fighting or just plain old devil fruit super efectiveness) would determine the outcome
which is also why I don't believe Rger was the single srongest character of his era and that Luffy will not be the single strongest character of this era
it's ofc entirely possible I'll jsut end up wrongs, but that is how I feel atm
