We have seen Mihawk vs a yonkou commander once before, at Marineford. There, Mihawk casually sent a long range attack at WB, which was just supposed to be a test. Jozu diverts it, but only after struggling. This shows that Mihawk is massively above Jozu, unless Jozu has some other reserved level of strength available, that he wasn't able to use in the war or in a group fight. But is there any indirect evidence to further back up Mihawk being way stronger than a yonkou commander?
Mihawk is a shichibukai, even though he travels the seas alone and lives alone. On his own, he has the power to rival the likes of Doflamingo's crew or Crocodile and those who have helped him. There's a chance that he isn't as solitary as he seems and maybe has had help from the likes of Shanks, but there's not really any strong evidence of it aside from him and Shanks being duelling buddies about a decade ago (Luffy was 7 when Shanks lost his arm and is 17 when he sets off in a barrel like Megan). This still doesn't really give us anything concrete though, apart from that he is probably the strongest shichibukai. Something interesting is that at Marineford, when standing with the other shichibukai, Mihawk says that he wants to know how strong WB is compared to "us". To me this indicates he believes he is definitely weaker than WB and maybe that there are other shichibukai who are near Mihawk's level of strength, although equally it could be that he was being humble, since in a war it's probably not best to badmouth your fellow soldiers by making out like you're stronger than them.
Based on where the plot of OP is likely eventually going (Luffy being PK, Zoro the strongest swordsman and a PK commander), Mihawk really should not be that far below the first mate of the PK, Prime (rib) Rayleigh. I believe that at the end of the series, Zoro will be at a yonkou level of strength, but Luffy will be on another level above even that. So, I believe that Mihawk is yonkou level and that Zoro wiil be only slightly above him, otherwise the fight to become established as WSS would be lame.
If Mihawk truly is the strongest swordsman (there's always a chance he isn't, since obviously he hasn't gone toe to toe with every big name swordsman, as shown by Vista saying he had always wanted to meet him), he should be stronger than Rayleigh, who was able to have a short, even fight with pre-skip Kizaru. Rayleigh is certainly a swordsman, as in his fight with Kizaru he exclusively used a sword.
Well, who else is a swordsman? Admiral Fujitora clearly is a swordsman, seeing as even when he uses his gravity powers he always takes out his sword (unless it's just like his version of a guide dog or something). Additionally, volume 70 of the manga contains a page that describes Law as a swordsman, so in that case Fujitora is likely a swordsman too, since he also regularly cuts things with his sword. Zoro's interest in Fujitora to me also shows that he is someone who would be considered a swordsman in One Piece's world.
So there is a decent amount of evidence to show that Mihawk is at least about on par with the admirals, at least pre-skip (I believe Fujitora is the weakest admiral, roughly on par with pre-skip Akainu), if not significantly stronger than then (for him to be clearly called the "WSS").
Now, how do admirals compare to a yonkou or to a yonkou commander? WB had the upper hand (but didn't outclass) Aokiji. This indicates than the yonkou are stronger than the admirals, but that an admiral can realistically fight with them, nut apart from that one time we don't have any clear contests. All we have is a weakened WB (confirmed by Marco and by his coughing up of blood) vs Akainu and the three admirals protecting the platform from WB's attack with their haki.
We have a bit more for yonkou commanders vs admirals though.
We've seen Akainu brush off Marco, even when Marco was really amped up after his friend's death. It's not like it was an intricate fight where Marco's anger would have hindered him either, it was a straight up power contest. It is OP, so it's not always about raw power and Marco's DF definitely means he can make up for a lack of power in other ways in a one on one fight.
We've also seen Marco fight evenly with Kizaru, until someone got seastone handcuffs on him. Along with that, there was Jozu vs Aokiji, where Aokiji froze Jozu solid, although again he was distracted. In both of these cases though, one moment of distraction was enough to strongly gain the upper hand.
These examples make it look like the commanders can fight with the pre-skip admirals, but they are generally significantly below them and can't afford to make mistakes at all. No admiral ever looked in trouble against a commander.
Everything points to Mihawk having a clear gap between him and the pre-skip admirals, so I believe he would take out two commander with medium difficulty. The commanders could escape with their lives and stall Mihawk, but I don't believe they could actually defeat him.
Mihawk fucks these fools up. I won't mind if there are some crazy strong yonkou commanders though, since they don't all have to be equal.