Luffy has never been betrayed, he brings people to his side, stop this nonsense.
9 YC3+ to Veteran level characters who are highly motivated suicide attack a DRUNK OFF-GUARD Kaido who suffers from specific Oden PTSD and they manage to give him superficial wounds while taking heavy damage themselves.
He sobers up, his zoan regen kicks in and that is pretty much pointless.
If he is on guard with his defenses up he becomes a lot harder to injure.
The whole "couldn't kill" aspect was never logical if you consider they could just chuck him in the ocean with seastone cuffs on, but we are talking in a state where he could presumably offer up some level of defense, in which case they cannot kill him because his serious defense and regen is too much.