What exactly is the narrative that Kaido grew significantly stronger over the 20 years based on?!?!
- Kaido did not appear to grow over the 5 years Oden spent dancing.
- We have not been told Kaido was not a Yonkou back then.
- We have not been told Kaidou grew stronger since then. We've only been told that he grew stronger since his Rocks days, but that's around two years before his battle with Oden.
The scabbards mentioned that they are stronger, we've been told Kaido is stronger than his Rocks days, so when characters grow stronger Oda tells us. Yet he didn't say anything about Kaido being stronger? On the contrary, Kaido becoming significantly stronger doesn't actually fit thematically. A huge point has been made about how no one could take Kaido's head in the 20 years since Oden's death, how only Enma has scarred Kaido, how only Oden could beat Kaido. None of that makes any sense if Kaido back then is significantly weaker. It makes no sense to hype up Enma and Oden if Oden fought an inferior Kaido. The narrative is not one of Kaido being this newly emergent threat, but of Kaido being a tyrant that has terrorised Wano for decades.
There is no narrative reason for current Kaido to be significantly stronger than 20 years ago, and it runs contrary to the narrative that Oda has set up. The only reason to insist that flashback Kaido is substantially inferior to his present self is to preserve some preferred powerscaling; well I've got news for you — Oda doesn't care about powerscaling — if you want to argue that current Kaido is stronger, then make narrative arguments for it, powerscaling arguments are utter unconvincing.