But King was mainly due to his hax.
Remember Zoro cut Kaido a yonkou and failed to do that to a yc1 ? Does it mean king over kaido ? Well it's true magma (a power king uses) is raping kaido right now, but come on let's wait for that
Nah. That is not how it works. Postskip zoro is not the same as even the zoro that fought killer let alone postskip one. Island to island people grow. Prime example is Law with infinite stamina who could casually use GK. And Zoro slept for one whole day post killer attack and he could take much higher attacks and could still fight. Could cut fire which he couldn't do postskip. He didn't master enma but it didn't create issue against Kaidou.