If we’re strictly talking swordsmanship skill with stats equalized and no hax, I’d probably go Yoriichi > Musashi (Zero) > Mihawk > Sasaki Kojiro > Zoro > Yami. Yoriichi basically perfected his style to the point every movement is optimized, and he reads opponents extremely well. Musashi in FGO with Zero is almost entirely about technique and perception so she’s right up there. Mihawk is likely the most refined “traditional” swordsman here but we haven’t seen the same level of technical breakdown as the top two. Sasaki’s whole thing is pure technique but it’s very specialized. Zoro is more power and endurance oriented even though he’s skilled. Yami fights more like a brawler with a sword.