How is what shanks use considered swordsmanship?? Without advance haki you can’t preform that attack no matter how good your sword skills are
vista wouldnt be able to even tho he’s a master swordsman with skills on par with mihawk
you need specific haki to preform that attack shanks is a swordsman but he has haki based attacks that mihawk can’t do
mihawk has sword skills that shanks can’t do
But as zoro bros said haki>>all