While Vista alone (which is ~YC3) already forced him into asking postponement?
How does this statement you made work? Are you saying Mihawk was fighting Vista and was overpowered and then decided to postpone it? From what i remember, he clashed with Vista while paying attention to Luffy through throughout the fight and then decided to just go back to chasing Luffy and then postponed his fight with Vista... I don't see where its shown that he was being overpowered... Half the fight thats shown is MIhawk literally not paying attention to Vista
If you're gonna say Mihawk SHOULD'VE Bodied Vista instantly, well then i can say Kaido SHOULD'VE bodied Luffy instantly too before Luffy even got one shot in... And you know what, Kaido could've done that... But then Kaido is a character who has pre estabished fighting styles and personality and how he fights is he lets the weaklings try something and when they disappoint him he ends it... Well Mihawk has a pre established fighting style, he let East blue Zoro literally push him back for most of the entire fight claiming he only uses the appropriate amount of effort according to he's facing... That's why Zoro didn't tank an Island level slash in East blue...
Therefore this Vista thing is pure baseless, its like You expect Mihawk to be like Akainu who literally foams at the mouth when he gets challenged and Mihawk MUST HAVE BEEN Going all out and just stalemated with Vista and Mihawk canceling the fight MUST BE him getting tired or something even though he was half paying attention the whole time... And Mihawk having the peersonality of someone who uses formal speaking and actually talks to the people hes fighting in a polite way is him being Scared of them since he isn't Spitting mad one liners "What King are you brat" like Kaido
So basically everyoen else is excused for having battle feats that match their personalities but Mihawk... Mihawk was just weak