When Oda mentioned Luffy will defeat Kaido, he made one thing clear: It will not be because "Luffy's punch is so strong". He even mentioned when Kaido first appeared, Luffy was not strong enough yet to defeat him. What exactly is Oda entailing by this? Well, we don't have to look far. The last opponent Luffy defeated at that time (Doflamingo), was defeated exactly because Luffy's punch "was so strong". In fact, every opponent Luffy has defeated so far he has been physically stronger than. Why is this significant? Well we know for a fact Luffy is not overall a better combatant than every opponent he's faced. With Crocodile this was obvious in Marineford, and with Enel Oda outright stated it. He said was lucky he was rubber. But nonetheless he was still stronger than both Crocodile/Enel physically. I recently made a thread outlining why Katakuri was a good milestone for Luffy. They are very similar in fighting style, and Luffy actually could use him as a measuring stick. With guys like Crocodile, Enel, Doflamingo, Moriah, Cracker, it's very hard for Luffy to measure his overall ability, simply because they fight very differently. What makes them good is not what makes Luffy good. https://orojackson.com/threads/katakuris-role-as-a-milestone-for-luffy.54835/#post-3500787 Just like, even if Zoro defeats Pica, Zoro still wants to develop as a swordsman, rather than just be a strong guy, Luffy even if he defeats all those dudes with dissimilar styles, still wants to develop primarily as a brawler more than anything. How Luffy defeats opponents is he negates/circumvents their DF ability (or DF combined with CoO in Enel's/Katakuri's cases) and/or he overpowers them physically. This seems kinda simple at first, but it's a very important point in the "Is Luffy stronger than the guys he beats?" debate. Whether he is a better overall combatant that those guys is up for debate, but what isn't, is that he is simply physically stronger. Kaido represents a new type of challenge. While before Luffy simply had to figure out some way around their DF/DF + CoO combo, and overpower them physically, Kaido is not that type of opponent. Even if you figure out some way around his possible DF (Zooan?), you cannot overpower Kaido physically. Luffy has defeated better overall fighters than him before (and I'd argue the gap between Croc/Enel and Luffy is much bigger than Luffy/Kaido now), but he has never defeated someone physically stronger than him.