We know for a fact that kaido has been defeated or captured numerous times, So it’s not the dude is completely undefeatable.
Next is your scaling of kinemon. Apart from law who has arguably a hax df power. Who else did we see that kinemon couldn’t defeat or even fight? We also know that 10 ppl went up against kaido’s previous army and almost won. 8 of those ppl were up against kaidos army are now facing kaido and kinemon was one of them. I’m not gonna day kinemon is some super strong samurai but it’s clear your estimation of how strong he is was misplaced.
Not only that, we’ve seen ashura doji, cat, dog, fish and denjiro display some actual combat prowess and then we know one is a white beard commander. We know they’re strong but bc kinemon didn’t do much or have the chances to do much you assumed he sucked.–- Update From New Post Merge ---
I thought about him too. He’d fit the mold perfectly. But poison and weaponry seem to be his thing.
Spot on. All the other scabbards think that Kinemon is their leader. It implies that he's the strongest among them.