Warlords are not a power tier, there is a clear disparity between their individual strength and Mihawk is by far the strongest among them. Mihawk wasn't a yonko because he didn't give a f**k, he only became a Warlord so people would leave him alone, and he only just now became a Yonko because the warlord system was abolished and people wouldn't leave him alone.
He is also the worlds greatest swordsman which is power based title, and "world's strongest" should give you some hint about his strength.
He is also future pirate king's right hand man's final opponent so him being anything bellow yonko level would be f*****g lame.
Seriosly I don't get why people are even trying to downplay him, do you want the story to suck so much? Are you even a fan of OP?