Honestly nobody should defend Mihawk for the sake of Zoro. If I remember correctly, didn't even Zoro reject Buggy?
Oda could have easily used this as an opportunity to wank Mihawk, making him the emperor instead. Ultimately proving that Mihawk is a rival or even stronger than Shanks. Instead, he made Mihawk a commander, proving once and for all that he forever lives in Shanks's shadow.