If he couldn't beat Shanks years ago, what makes you think he can now? Utterly ridiculous.
The reverse is also true.
If Shanks couldn’t beat Mihawk years ago when Shanks had both arms, what makes you think he can beat Mihawk now? We know that since he fought Shanks, Mihawk defeated other sword masters and turned his blade black.
He is also acknowledged as the WSS while Shanks is not despite supposedly filling all criteria for the title (being strong, being a swordsman), while Mihawk isn’t a Yonko because he doesn’t have a crew or territory which are required for the title.
Mihawk isn’t in the conversation for Yonko because he doesn’t fulfill the basic requirements, while Shanks has never been referred to as the WSS because he is simply weaker than Mihawk.
Strength is the only requirement for WSS. Strength is not even close to the only requirement for Yonko. Marco was almost a Yonko ffs lol.