What exactly defines a swordsman in the One Piece world? To answer this question you need to understand how Oda want you to perceive a swordsman.
Was it this clown in Cabiji who rode a unicycle, and practiced circus tricks?
Was it this fish with 6 arms who's strong even
without the use of swords?
Or was it this man made out of metal who claimed he was an assassin, and not a swordsman? Only for Zoro to brand him as such in the first confrontation.
Or even this bitch with wings who utilized a whip like weapon capable of taking any form, rather then a conventional sword?
Was it also this giraffe-man who's mastered the 6 styles and was already a superhuman in base?
I can go on and on and include the likes of Pica and even Fujitora who's literally a top tier
swordsman with an op df. Oda considers them all to be swordsmen. So why wouldn't a guy equipped with a cursed sword, who uses it for everything combat related not be considered a swordsman?
Regardless of who they are, and what powers they hold if they're considered a swordsman by Oda, they will be below Zoro come EOS, just all all his previous opponents.
That means Shanks. That means Mihawk. And that also means Law.