It sounds like the direct opposite to me.
Luffy vs Kaido has been gone for a few chapters. When the manga returns to that battle Luffy is using a new attack and say he won't stop attacking until he runs out of energy. That doesn't sound like is Kaido about to be defeated. It sounds like Luffy is about to run out of energy and needs somebody (Zoro) to step in to give Luffy time to recover again.
Big Mom received two and a half chapters before she was defeated and even then bombs were needed to finish her off. Oda it's not about to have Luffy defeat Kaido in a half a chapter.
how did zoro get there? What is the purpose?
he won't be able to get there, marco is busy with izo somewhere, everyone at this moment is busy with something or someone.
what purpose? null, zoro has already gone to the roof, he even defeated a dragon in the form of an attack, zoro can barely move, he is very far from the roof, unless you suggest that luffy's fight can move to where zoro is lying, i don't see How can Zoro be relevant or have a turning point at this point, another miracle medicine?
the only way zoro could be there is if the whole gang goes there, from nami to sanji, oars type, but that's not happening either.