I find him, Jozu and Marco kind of hard to place. I'm one of the few who actually thinks Jozu is stronger than Doffy, though

But honestly, I don't think Zoro is on that level yet. Vista even clashed with Mihawk and walked away with no injuries. But they obviously weren't going all out. Actually, we haven't seen Zoro's strongest move yet, either. I'm waiting for him to use Asura and just instantly becoming Admiral level xD
But I definitely don't see him fighting a 1st Mate. Imo, Zoro has to help with defeating Kaido. Well, it depends on who will take part in this. If theories are correct and Drake joins, then I can picture Luffy, Law and Drake fighting Kaido together, while Zoro, etc. handle the Commanders.
Poor guy... He needs to get some.