Wrong section but personally i believe he is for some reasons:
- Mihawk told to Shanks at the start of the serie that he has no interest in settling his battle with a man with just one arm. Settle here mean their battles in the past was never settled, so they were probably on the same level
- They were equals when Shanks had both his arms, now Shanks lost one, so he should be weaker at least in swordsmanship
- Shanks is a swordman and Mihawk is known to be the strongest swordman
- Mihawk is the strongest warlord which is said to represent the 3rd power to balance Word Government and Yonkous