Well about the fight vs. King.. it is on Oda.
If he wants to portray Luffy and Zoro vs Kaido he will make ZorovKing a low to mid difficulty fight.
Probably mid and no Asura involved (or any additional new power up of any kind.)
its not about just the difficulty , if oda wanted to stick with the time that luffy needed to to win against commanders (11 hours with cracker , more than 12 hours with kata ) then the calamity will demand a long time to fall whither oda show most of it or skip it .
unless the time with cracker & kata was just for plot to move on .
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did you think then zoro got around king level after TS if he gonna take him down without going all out ?!
in my opinoion maybe zoro will not show all his new moves but vs king he'll use the strongest of them and improve during the fight as learning how to cut fire , this is king what we are talking about if kata gave luffy hell , then what do think king will do to zoro ?!
even his bounty maybe is above kata 500 mil or more .
zoro vs kaidou hmm, i dont think asura is the solution so no benefit from saving it to kaidou, its how oden manga to cut him ?
if zoro learned how then he can do it without asura . but really how oden did it and how will zoro learn it ?