The fact that Luffy likely won’t get a clean decisive victory over him is further proof. I like that Oda did this, because now it’ll make perfect sense when Luffy proceeds to struggle against opponents weaker than Kaido post-Wano.
The only living characters to surpass Kaido during the story will be Blackbeard and Luffy
He will get a decisive victory and will be deemed to be stronger than him by the world.
Luffy is like the other yonkos (aside from Shanks) in that he has a very sloppy personality and is slow to use his full strength.
This leads to shenanigans like Luffy getting stalled by people like Apoo/Ulti, Big Mom getting stalled out by the strawhats multiple times, getting knocked off Wano etc, BB nearly getting killed by Magellan and hit by pre-ts Luffy, Kaido getting disarmed by the scabbards and cut by Zoro.
This sloppy PIS will suffice for the small times before BB/ Imu