If Shanks never existed in OP, Mihawk by portrayal is definitely not on the Yonkou/Admiral Tier.
He has been absolutely stalemated by Vista, it wasn't even hinted that Vista was struggling. Not only that WB selected Marco to protect Luffy. Marco then proceeds to select Vista to protect Luffy. In terms of pure hierarchy, this is looking ridiculously bad for Mihawk since when the admirals stepped up to fight Luffy, Marco himself intervened (kicking away Aokiji). Could you imagine Marco directly Vista to stop Kaido, Big Mom and Shanks?
Before the war even started, there was even some level of portrayal between Doflamingo and Mihawk. When Mihawk stepped up to attack WB with his slash, he comments "I want to see the distance between us and that man". Who is "us"? Well seeing as how him and Doffy were chatting just before, us correlates to Doffy and Hawk, (even Boa since she was portrayed on that level during MF). Now obviously Mihawk > Doffy/Boa, but to even put those other two in the same breath as him is telling. Again, substitute Mihawk with Shanks/Big Mom/Kaido, there is just no way they say something like that. Not only that, him recognizing himself as lesser than WB in speech was telling to me. Shanks stepped up on WB's boat and immediately commanded respect from everyone, he went directly to WB and clashed with him on equal terms. They're portrayal with regards to WB is completely different. Shanks clashes with him as an equal, whereas Mihawk with him as a test for himself.
People speculated that when Shanks stopped Kaidou from intercepting WB, that he bargained with him or some shit, (even though it was noted that they had skirmished). Kaidou confirms in this later chapter, that Shanks is about that life and is among those able to fight him (and possibly defeat him). People also speculated that the 4 Yonkou are only Yonkou because of their influence... lol. We had two of the Yonkou as the epitome of fighting power themselves and somehow the other two, or Shanks namely is supposed to be a step below these guys? Naw.
Mihawk by his own powerscaling feats and portrayal between characters inside the manga is poor. He is more comparable to the YC than the Yonkou themselves. His only saving grace is Shanks, who is more than likely not encompassed by the WSS title. If Shanks is revealed to be the current WSM, a lot of people are going to cry saying it doesn't make sense, although it should be apparent at this moment that Shanks > Hawk.