In one of the interviews, Oda said that he doesn’t know how Luffy should win because Kaido is incredibily powerful.
Oda: “When Kaido appeared for the first time, I said that Luffy can’t defeat such a strong character yet. And I’m yet to know how Luffy would defeat Kaido. Probably my audience will not be satisfied if the reason for defeating Kaido is just because Luffy’s punch is so strong. Luffy and I have to find a solution somehow.”
As far as we know, the potential solution to Luffy beating Kaido is Ryou.
Oda had to have known this was the solution since we know how much Oda plans out the story in advance as shown by his foreshadowings in the series and because he foreshadowed Ryou from Amazon Lily with Boa Marigold so he knew he was going to reintroduce it back into the story for Luffy to master.
Although Oda doesn’t want Luffy to win because his punch is so strong, in a way he is, through Ryou as using Emission and Internal Destruction is much supeior to his regular attacks.
The difference is Ryou requires the user to not actually ‘try too hard’ and let their haki flow through them naturally. Hyogoro even mentioned that Luffy shouldn’t “press too hard” when activiating Ryou. It’s kinda ironic.
*Theory by SL2310
