Oh, please, don't play dumb... I know the narrative strength of One Piece lately has been on par with Winnie the Pooh, especially when it comes to the main crew, but surely not all your nerve and brain cells have deteriorated. Kaidou fought the Akazaya Nine for at least 10 chapters, and each of them managed to injure him. Then he fought alongside Big Mom against five members of the Worst Generation for 15-20 chapters, where, except for Kid, they all managed to injure or hurt him. Then, when Luffy got knocked down the second time, Kaidou fought with his son, Yamato, for several chapters, who was not only able to injure him but also knew the special Conqueror's Haki. And when Luffy got back into the picture, even Momonosuke took a few bites at him. And yet you can claim with a straight face that every other character's attacks just bounced off Kaidou, but whenever Luffy attacked, it just happened to hurt a lot and really wore Kaidou down? Yes, Kaidou didn't go down from any of those attacks, and none of them caused him so much pain that he would drop to his knees even for a few minutes, but the same can be said about Luffy. Except for his final attack, after every single one, Kaidou just kept fighting without any problem.