Did Oden have advanced COA? I thought his cut was simply just his insane hardening and how physically strong he was.
And since Oda also loves to dehype a character on the one moment AND extremely hypes the same character on another one, I can imagine that Kaido learned advanced CoA as well.
After all, the Scabbards only know that Kaido 20 years ago but not really current Kaido.
But, I agree. If Luffy is learning these things in short order, theres no excuse for other top tiers to not have it.
"Hah! I learned the ability to hurt you, Kaido!
*hurts Kaido extremely and then pummels him*
"See? And now you are going to lose!"
I don't think it's that simple. If Luffy can just easily injure Kaido like that, why should he need help from other characters?
Therefore, Kaido has some trumpcard as well in which he should be still vastly superior to Luffy 1vs1.