Maybe lack of panels and feats.
Like Roger, Shanks, WB, Kaido, Dragon, BM honestly.
All this debate when no top tier beside Aka Inu defeated another top tier in 1 vs 1. But at least Roger vs Wb and Shanks vs Mihawk happened and the conclusion is at least draw. But the line about Mihawk's vivre card that he is waiting for someone superior than his rival shanks means that Zoro will face Mihawk when Zoro will be stronger than Shanks. It's enough to say that WSS Zoro will be above Shanks and Mihawk.
Love how people say Mihawk didn't fight Shanks after he became Yonkou, who told you that ?
Oda said Shanks strengh didn't change so Mihawk has probably defeated Shanks to become WSS.
Oda is not dumb like you boys to change his point of views every weeks and when a character just appears LOL.
And who told you that Mihawk became WSS before Shanks becoming Yonkou ? He became maybe 5 years ago after defeating Shanks ? Who knows ?
Because he lacks some feats mean WSS is not legit ? Kaido the WSC was defeated 7 times, what a hype for the strongest of all living ...
Mihawk is the only living character that no one ever touched him, didn't have any scar, never bled, the only one who has black blade.
Said by Wb himself that only few became legends and implied that Shanks and Mihawk are part of it. If EOS BB is gonna be the strongest opponent for Luffy, Mihawk is gonna be the strongest opponent for Zoro who will have defeated a yc1, low top tier (shiryu) and probably an admiral also before Mihawk.