imo the sheer fact Mihawk isn't a yonko in of itself puts him below shanks.
Shanks is portrayed as the strongest conqueror. The fact Mihawk lets Buggy call himself captain is proof Mihawk either isn't a conqueror, or if he is, he isn't a very good one.
This isn't to say Mihawk isn't a top tier, he clearly has some top tier portrayal. But it puts him in the same vein as Ryokugyu. Possibly even worst, as all the admirals fought stronger characters in MF.
Also, no yonko(bar buggy) would have gotten stalled by vista. Queen got put on his ass when he tried to challenge O-Lin directly, had to use a cheap shot against her, and literally shat his pants when she recovered her memories. Kaido 1 shot Luffy before and after he got ACoA.
Overall, the fact Oda uses him to further buggy's gag is just one more in the pile of evidence that Mihawk is just a low top tier. Definitely impressive in his own right, on another level from most YCs, but definitely not top 5 like zoro fans claim.