Shanks being stronger than Mihawk doesn't affect Zoro's dream

The reason it doesn't affect is because Shank's strength has never been something Zoro cared about, Shanks is usually someone Luffy wants to surpass or beat so whether he is stronger than Mihawk is something that will never be brought up.

What would happen is that Shanks will problaby be defeated at some point and maybe die and so would Mihawk when he loses to Zoro. And who is stronger would generally never be brought up, Oda doesn't seem to care that much about powerscaling.

There is nothing stopping Oda from giving Shanks some of the best feats in the verse by EOS like he has done until right now while giving Mihawk mediocre feats like he has done until now. Then Zoro beats Mihawk, gets the title and that's where everything ends. It's not like anyone would question Zoro's title in the story

And this is problaby what will happen given Shanks was in the 1121 panel of the most relevant characters which implies he problaby will keep getting insane feats until his eventual defeat. But Mihawk not being there means most likely Oda will give him the treatment he gave him in Marineford making him clash with lesser opponents and honestly not looking very good. At the end Oda has no reason to give Mihawk good feats because he simply isn't important to the overall plot, so he can Mihawk do anything impressive until he loses to Zoro and his title.