All the "evidence" supporting ZKK is cherry picked moments that are misconstrued to support a delusional theory.
It does not matter if people saw Zoro cut King. In Monsters, Ryuma cut the dragon while the town was completely deserted and only a single girl saw it happen.
If Yamato is not strong enough to kill Kaido, than neither is Zoro. But that aside, Yamato beating Kaido is more likely because
A. Yamato is the next Strawhat
B. Kaido is her father
Kaido is a devil fruit user. All he has to do to kill himself is to jump in the water. The reason he hasn't done this is that he wants his death to be glorious.
That was the point of him cutting King's Dragon
No cherry picking just you ignoring any and all information that supports ZKK.
We find out not only does Zoro look like Ryuma but has one eye like him and Hyou wonders if that's fate and you call it cherry picking. It's not hard to see Oda wrote that for a reason and you just chose to ignore it because it goes against your headcannon.
Kaido's DF is a fish DF model Dragon. Since fish can breathe underwater Kaido should be able to do the same so he won't be able to drown himself.
The manga doesn't consider cutting a fire technique that's shaped like a dragon the equivalent to cutting a dragon.
Zoro is stronger than Yamato and has greater AP.