This makes Mihawk look so bad. There should have been nothing stopping him from one shotting Vista. Literally no reason to postpone the fight. He just don't got it like that.
But it doesn't really, unless you believe Mihawk isn't a top-tier.
You can't chastise Mihawk for not putting down a YC3 and call him a top-tier at the same time - these two actions are mutually exclusive. Because no serious top-tier would ever struggle with a YC3 - it isn't possible, period. Even a serious current Zoro would one-shot Jack.
So unless you believe that Mihawk isn't a top-tier and Zoro has already surpassed him, it doesn't make sense to bring up Vista. Because what exactly is your point?
Mihawk has been reiterated as the strongest swordsman in a direct comparison with Shanks, who we now know without a shadow of a doubt is a swordsman. In the same chapter, Mihawk turned down the position of Yonko in favour of a peaceful life. His portrayal as a top-tier is undeniable, so bringing up Mihawk vs Vista is like chastising Fujitora for being bruised by Dressrosa G2/3 Luffy. It doesn't make sense because we all know neither Luffy nor Vista were ever of any real threat.
Shanks literally got his arm bitten off by a fodder sea king. You talking about postponing a fight with Vista whilst Shanks is getting maimed by fodder lool. Let's not be selective now, Shanks' low-end feat is infinitely worse.