How has it been proven wrong when the fight isn’t over yet? And how do you know this is all Luffy has to offer? Remember when he was struggling against Doflamingo and then brought out Gear 4th? What if he brings out Gear 5? What if Hawkins gives him a crazy power up? There are plenty of ways for Oda to make Luffy hurt Kaido. Don’t bet against the main character.