The ZKK theory is not Zoro vs Kaido Round 2. They are not related. When you guys understand the difference then I'll have a proper conversation with you.
Marco mentioned fighting Kaido already back in Chapter 999, this was after he threw Zoro to the roof. He has been stuck on the performance floor helping. That's it. Nothing is even suggesting he will fight King for the remainder of the arc.
It's not about what "services" Zoro. It's about what "services" the story. You guys don't pay attention to dialogue. Zoro said to leave Kaido to Luffy already lol. The story has only told you guys a 100 times already that Luffy will beat Kaido.
By the time Zoro is done with Kaido the odds King will still be around and at the same time Zoro will take him on are about as tiny as a bacteria.