Have you read Mihawk's fight with Zoro???
Cause if you did, you would realize that Mihawk is unlike all other brutes who go all out to hunt a rabbit.
Mihawk could have finished Zoro in one attack. yet, he chose to entertain himself because he's amused by this kid who is challenging him for the first time. He wants to see his swordsmanship and what he can do. So, he gets out his small knife and simply allows Zoro to use ALLL of his moves and still rendering him useless instead of just oneshotting him.
Mihawk is that damn bored that when he sees a promising swordsman, he wants to test this character and see what they can do
It was made clear when Mihawk met Vista, it was THEIR FIRST TIME. Because Vista himself said it "So, you've heard of me?"
And Mihawk replied "I would be ignorant if I didn't hear about your name"
And this may be a non-manga because it was only shown in anime. But there was a dialog between them which also emphasized that on Mihawk.
Mihawk says to Vista: Best swordsman on WB ship, will you not show me your flower blade style?
Vista: take a good grasp, Rose rondo!
The point is that, Mihawk is that damn bored who's looking for someone who can either be a challenge of him right now, ORRRR if he's not able to do it now, they are AT LEAST promising enough to develop later and pose a challenge later. Zoro and Vista belonged to the latter group.
Mihawk was interested and amused by them, he simply didn't go all out wiping them out with one big attack like other brutes (Kaido as an example who finished Luffy with a big named attack)