How is Mihawk winning this? No, just no. If Mihawk was capable of defeating Issho Mid-Diff, that would mean he is capable of defeating Akainu High-Diff, which is obviously false. Issho wins this High-Diff. Mihawk is around as strong as Marco, who is not as strong as any Admiral we have seen yet.
Akainu >= Kuzan >= Kizaru >= Issho >= Marco = Mihawk.