Damn I never thought about this. Kaido low diffed Luffy from the start
I think in typical Oda fashion it was written to hyperbolize the
"One v One always bet on Kaido".
Luffy was
technically thrashing Kaido while in his inebriated state. But then once Kaido got serious, he ended it.
And from Kaido's perspective he had just as much anger against Luffy, as Luffy did on him.
Law and Luffy destroyed Doffy and Smile, which was Kaido's way to build a formidable army on his war path against the world.
When some little midget and his friends comes and fucks that up, of course he's gonna be pissed off.
Yonko need to be ridiculously strong for maintaining territory and pull on the entire world.
The WG have to make preparation for them for a reason.
And to explain Luffy's sudden exponential strength growth, we can just apply the Laws of Shounen Logic where 2 weeks focused training + willpower + PK Inherited Will = Ryuo at the Highest Level and Durability times 5. This explains why Luffy is tanking hits now. And this is the most we would have gotten from Oda. (I'm sure he had more in the bag, but that's where editors and Shounen Jump chimed in to decrease the quantity of training montages)
In order for a long running story to progress, Oda had to cut corners. Its not flawless writing but it still follows a Palpable strength progression. In my opinion it was done well, with an already stagnating in quality story, I'm surprised we even got this, given Oda's track record of handing power ups.