I like how everyone has to pretend it isn’t obvious Shanks has a devil fruit sword like his brother (and likely father)
You don’t need to know martial art to punch or kick someone. Big mom, king, Kizaru, etc don’t have a formal fighting style despite being skilled enough with swords
You’re talking about the same Shanks Mihawk couldn’t beat and fruitless Blackbeard scarred
Shanks being skilled with a sword doesn’t limit him to just swordsmanship. Especially considering he lost his dominant arm and has a very obvious devil fruit sword