Mihawk has a lower bounty, was portrayed fighting YC and looking up to measure the distance from WB and is destined to ultimately fight a subordinate.
Shanks is a CoC SPECIALIST like Luffy, Zoro may have CoC but he isn't a specialist and is so limited as CoC cannot be trained.
Mihawk was testing WB strength and didn't even bother to use a name attack or haki and it still required the WBP member with the strongest defense to stop his casual attack.
A casual Mihawk was fighting a WB YC who couldn't even touch him even though he wasn't even focused on him. Crocodile failed to hit him with surprise attack. Marineford was about showing us what a casual Mihawk could do.
Big Mom and Kaido combined attack was counter by Zoro alone. Kaido had to use hybrid mode to face Yamato, wo was beat easily by GB who didn't even want to fight her. She was begging for help. Big Mom had a even clash with a YC, ran away and said she didn't have no power to win.
Mihawk could have been the leader but chose not to so he could move unnoticed and work for the shadows easier. Mihawk has incredible strength and intelligence.