Swordsmanship has the best feats yet. While you refer to Kaido being buried in Magma and his status being unknown to us. That's not how it works buddy. I'm sorry.
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.
And ofc Kaido meeting his hand by Magma and not the blade.
A casual haki-less Magma punch critically wounds people while a casual sword swing can't even cut Kaku's pants who isn't using any sort of defence himself.
Magma is the most lethal ability in the OP world.