It is funny, back then fanboys said Zoro was holding back, now when ashura showed in the story and Kaido tank it like a boss, fanboys said nerfed Ashura
Too many excuses and headcanon. Why don't you accept Oda just want to show that zoro's current power is not ready for Kaido. Zoro already showed great feats but let's not exaggerating things.
In the end Luffy Will always be stronger than Zoro