I get it, post ts felt different. the cast is too big most of the arcs. And some fights will be rushed or resumed offscreen.
As for this fight, Kaido is the one fooling around. He underestimated his opponents, tanking their attacks not even trying to defend himself. (I dont know if it is...
Yeah, but Luffy's not the only one. Zoro mentioned to Kaku that he was way stronger than before, and Sanji came out with DJ. So it's not surprising that Killer comes out with a new skill after his defeat against Kaido. (Of course Luffy is the MC, his progress is better than the others.) But the...
The advanced CoA might be confusing indeed.
We got the regular one (low level) - hardening - invisible armor (High level) - and the "internal destruction" (just like gentle fist, Luffy and Rayleigh are the only user so far).
The invisible armor is already enough to damage Kaido, doing less...