Some people here fail to realize, that Yonkos don't see each other and are neither enemies/allies of each other. They are neutral. Maybe you could make the argument that their individual strength works as a DETERRENT, but they rarely, if at all see each other.
This notion that Yonkos are constantly engaging in these amazing 1 v. 1 clashes is pure fanfic. And even if they do, we saw that even someone like Jinbe can fight and escape from Big Mom.
Kaido was shook when it came to Big Mom and 1 ship.
WB was the WSS and he didn't dare go against Kaido.
Fighting head on against another Yonko is a recipe for destruction, even if you're a Yonko yourself.
Ok sweet. Kaido is not an Emperor according to you.
2 Yonko fighting one another is assured mutual destruction.