Mihawk greatest fight was Shanks from 12 years ago, 6 years before he becomes Yonko.
Vista never clashed with him until MF.
No swordman or another top tier of rename clashed with Mihawk for what we know.
His visual feats are way below Admirals who can clash with a guy who can toy with a part of the ocean + tectonic plates.
Yonko clashing split the "heavens" while Mihawk clashing with Vista did nothing.
His title doesnt mean anything aside that he is the most skilled swordsman at most, not the strongest among swordsman since many swordman doesn't focus on swordsmanship entirely because they have devil fruits or they can make up with better Haki.
Facts / feats > everything else.
You are dwelling in the past instead of looking into the future...
Look at who Mihawk will face - Zoro, who will have heads of top tiers in a bag by the time he fights Mihawk.
Oda is making Zoro the greatest swordsman ever and the hardest challenge he will give him is going to be Mihawk.
Not Vista, not Shanks, not an Admiral or anyone else.
Yonkos can split the heavens all they want, when that feat actually does something useful in a fight, I might praise it.
His title means exactly what it means - the strongest swordsman in the world, above any other swordsman.
Your mistake is thinking that devil fruits are superior to swords or that someone has better haki than Mihawk.
You can wank feats but you will have to do a 180° when Mihawk shows his, which will make you into a bad power scaler.