Zoro get's a power boost in his fight with King in order to defeat him, and it's that power boost that pushes Zoro at the level required to be able to open Kaido's scar.
Zoro can have top tier cutting ability while overall not being top tier, that's perfectly fine. Katakuri has top tier CoO while he is not overall top tier.
After his fight with King, all Zoro needs to do is to have the remaining stamina to get to Kaido, and land one attack that opens his scar before collapsing.
Zoro and Sanji always still have enough stamina to run around and even get into fights after their end of the arc main fights. Like it was the case in Alabasta or Enies Lobby, so can be the case in Wano.
You actually believe Zoro will have more power than the all the scabbards AFTER an extreme diff fight?
Wow like even I can't say that. Seriously.
Zoro being able to walk after beating kaku doesn't mean he can then fight another substantially strong person. The times Zoro has fought a stronger person After his main fight was Thriller bark and a skypiea where Zoro just mid diffed both his opponents
I'm telling you, this scenario you're proposing means Zoro mid diffs king. Plain and simple. Like there's no way Zoro can be that strong after an extreme diff. It's no longer an extreme diff if zoro is pulling out Admiral level ap afterwards.
I don't know what to tell you. It just isn't. The definition of extreme diff is that it's a complete drain. Being able to scatter fodder afterwards is just that. Scattering fodder. You can't then be strong enough to do shot like cutting Kaido and say that was an extreme diff