Kaido is described as the strongest creature to exist on land, air, and sea.
…Kaido could not defeat Luffy’s will.
Every time after his physical defeat, Luffy’s strong will immediately manifests itself in some form to challenge Kaido once again.
Now let’s look at what we know about Kaido: he is completely empty inside to the point he tries to kill himself but survives so he wants to start a big war so that he can die like Whitebeard and otherwise spends all his time drinking.
I think that the duality of Kaido is that though he is the strongest creature he does not possess the strength that he saw these people have:
Strength that runs greater than just physical. One of the spirit, one that somehow lives on even after they have died, been crushed, defeated.
And I believe it is this that Kaido is trying to replicate and understand but he cannot as his means are superficial, he wants a war that he does not care about in the least, he wants to die for something but he does not believe in a single thing.