If the story is going to cross guild faces strawhats in the race for the one piece, Mihawk vs Zoro would happen before the final war, right? If Mihawk is not zoro last opponent, but actually is Venus, do you think that Venus can be stronger than Mihawk?
Just like how Kaidou is > Kizaru.
Or Daz Bones > Ohm/Braham.
Villains coming later doesnt make them stronger automatically.