Maybe Kaido didn't take damage from Kidd or Law's attacks, but he definitely didn't take damage from Luffy's Kong Gun. He didn't even grunt in pain.
It's possible. Then it would mean Luffy didn't use adv CoA. Because G4>G3, if he can hurt Kaido in G3 with adv CoA, it's impossible that he can't hurt him with G4. It wouldn't make any sense.
But anyway I don't expect anything major from Luffy in the next chapters, he will be on Law and Kidd level (maybe even slightly below them) until these 2 are defeated and then he will remember how to be stronger.
It's just how plot works for Luffy.
Also I don't understand how Kaido can feel pain from 3 rocks being thrown at him when he jumped from 10000 meters and just had a migraine. Now suddenly rocks hurt him. I doubt the force Law applied to the rocks is stronger then the impact created by a 10000 meters fall.
Oda is trying too hard to make Kidd and Law relevant and forgot what he wrote a few chapters ago.