Well we gotta remember Kaido has zoan regeneration. Attack became scar pretty soon but in the same situation any normal non ancient zoan regen character would have died out of blood loss alone.
Blood loss death is an actual thing in One Piece btw.
I just see Zoro's Ashura as Gamma Knife, when Zoro landed it, wound was deep and Kaido was heavy nerf and even Luffy's nameless attacks were doing damage
But later as the attack healed and became a scar, Kaido was no selling Supreme King Kong Gun.
Like when Ashura landed damage was about 60 to 70%, Kaido was close to falling but it wasn't enough and he healed.