All we know for now is that 5% HP Zoro performed a feat only Oden was able to do. A fresher Zoro had the offensive power to stop the strongest attack in the series; both feats have been his upper limit of strength at the time.
Take that in to account and watch how the King fight plays out. I don't want to assign a mid diff or high diff to it yet, we are not sure quite how strong King is tbh.