The Namek arc of Dragon Ball, both Vegeta and Piccolo had more motivation to defeat Frieza, but it was Goku who did so. Just like how Law had more motivation to defeat Doflamingo. Because the main hero defeats the main villain in Shonen.
So, if anyone really thought Kaido, the strongest pirate the crew faced at that point wasn't actually going to be defeated by Luffy, they are a slobbering idiot.