All he did was use a Haki blast to scare him.. This is like arguing Zoro isn't a swordsman because he defeated Monet by scaring her
Shanks sent an island wide CoC beam targeting GB.
Im not arguing Shanks isnt a swordsman. Just that his style relies on more than just swordsmanship.
I mean the guy doesn’t even use standard slashes, he uses shockwaves. You can argue divine departure uses swordsmanship as a sword is involved. But the shockwave itself isn’t swordsmanship, even Garp and Koby can do that with a punch.