Magma has consistently been portrayed as superior to swordsmanship even in feats.
- Akainu melting WB's head off and punching a whole through him.
- King a fellow sword user counting on his Magma-like flames as his last resort.
- Kaido using Magma/Flame Dragon mode hoping it'll Burn down Luffy's fist and not push it back via Adv CoC.
- Whitebeard has poor durability.
- King is a mediocre swordsman, he has no advanced techniques.
- Kaido isn't a swordsman, he uses blunt strikes with his club.
Yes, outside of Haki, Magma >>> swords. Yet swords get massively boosted by Haki (both Ryuo and Haoshoku), Magma has not displayed that. That results in Kaido being clapped out of the sky with one blow by swordsmanship, Zoro ripping through King, his wing ans hakified sword and Shiryu, who probably wasn't even a top tier preskip, being Magellan's equal, who has the poison fruit. Swordsmanship has shown to tear through extremely tough defenses and break haki defenses and hakified weapons.
Sure, if Haoshoku can give Magma as much of a boost as swordsmanship, Magma >> swords. Not the case though.