You just posted picture that shows Hachi as swordsman, the guy who used his punches as final attack vs Zolo, and used a body slam vs. Zolo during the fight similar to how Alber fought. Also Roger, who used a pistol vs. Shiki. And Rayleigh, who trained Luffy without even carrying his sword along with him.
Swordsmanship is just a style of fighting, we've seen Law is literally trained at other martials arts as well, he can mix it all. No one said Shanks can't use anything else as well. Its not forbidden lmao.
That's saying like an MMA fighter who can strike, wrestle and grapple, is a striker. Yes, he can also do other things, he is also a wrestler and grappler, that doesn't mean he isn't allow to use other techniques.
Pica used a sword at first, then dropped it and focused on his Haki. Zolo admitted he couldn't cut Pica if Pica had greater Haki.
If Shanks has greater Haki level than Mihawk, (which he has) what even fodder Pica tried to do is too easy for someone like Shanks to do.