Just the king fight look at Zoro. Zoro is a much stronger swordsman from gaining better haki. Swordsmanship is op is the abilities you can use with a sword which is why calling meteors, using ice, using fire, using haki, summoning 2 each head and 2 sets of arms, making cracker soliders, etc are all viewed by the op world as swordsmanship. It isn't like our world where we don't have superpowers and can only swing a sword so our swordsmanship. The swordsmanship in op is abilities with a sword.
I Don't get to this day why you'd try to base our worlds standards to one. Like we don't have human fish hybrids that do karate.