But there's more to sworsmanship than just haki right?
Or else Roger, Shanks, and even WB would've made their weapons black blade.
I'm just saying Mihawk who's strength is synonymous to Yoru is peak swordsmanship rather than Nasu who'd probably still be top tier without his sword, meaning he'll not rely much on his sword as much as Mihawk.
But if Nasu has a black blade, well, I don't think there would be a doubt he is the stronger swordsman.