Again, do you know how he obtained the title to begin with?
Oda is literally famous for having worldbuilding and backstory for so many of his characters and all it would take would be one flashback to where we see Mihawk beat the previous WSS and have a similar journey to Zoro to show us that it doesn't mean he's actually beaten everyone.
Stop using "Oda said he's the strongest" as if y'all knew what Oda is planning either, it means nothing until he shows us him defeating everyone.