I really dunno about using Mihawk in matches when we don't even know how strong he really is.
If he wasn't holding back at Marineford, and his comments seemed to indicate he was sorry to Shanks for not doing so, then he isn't touching Luffy any more now that his fight against Katakuri dramatically improved his precognitive abilities and the timeskip in general made Luffy significantly faster and more agile.
Plus, like, we have no idea how much damage someone like Mihawk can take, either. Luffy's punches are now strong enough to do serious damage to someone like Kaidou, so would Mihawk be able to take those kinds of hits at all?
Mihawk defeats Luffy.
Marco doesn't need to defeat Yamato, he just needs to stall her.
If he can stall emperors and admirals just fine (until other people show up), then he should definitely be able to do the same with Yamato.
Then, Mihawk can defeat her.