Honestly, at this point, it doesn't really even matter what the title is for. It doesn't matter how Mihawk got it. Or how much of Shanks' fighting style comes from haki and how much he can do irrelevant to a blade, etc.
WSS is Zoro's ambition. And Zoro is far more important than either of these two characters.
And this is how Zoro perceives his ambition and this is what Zoro wants to become:
As long as Shanks is a swordsman in name, calls himself a swordsman, or is officially dubbed as such by Oda, he simply cannot EoS Zoro lol.
And there's no reason to assume the title Zoro wants to hold somehow has different fundamental meaning than the one Oda says Mihawk holds in both name and actuality.