A True Swordsman can Choose what to Cut
A True Swordsman has Sword-Style Techniques
A True Swordsman can use Flying Slashes
A True Swordsman tames Meito Swords
If any of these Apply, then you're a Swordsman
If All of these Apply, then you're a Skilled/Great Swordsman
If your Haki & Physical Stats & Sword-Style are Pretty Strong then you're a Master Swordsman
If you have Adv. CoC then you're among Strongest Master Swordsmen
Only when you Perfect everything, can you become World's Greatest Swordsman
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King only carries a Sword, did He use a Sword-Style Technique? No
What about Pica? No
Queen or Jack? No
Kizaru or Aokiji? No
... etc
So these are not Swordsmen until Proven Otherwise
Roger tamed Supreme Blade Sword, Named his Son after it, his Crewmember inherited his Fighting Style & went on to Rival WSS, and his Signature Attack is literally a Sword-Style Technique. Roger was 100% a Master Swordsman