So you don't think it's possible that Shanks base fighting style is swordmanship, like he used to be before loosing his arm. (this style is enough for 95% of his battles) (like Luffy base form)
But when he get's serious he uses some other fighting stance which he developed after he lost his arm. (which also give him the strenght to become a Yonko.) (like Luffy's gear 5)
Most people who follow one style primarily don't switch their fighting style to something completely different when they're serious. Even the mele fighters, who are more likely to have different styles, only use stronger abilities when they get serious. Like, Big Mom, combining her homies, for example.
Look at Kaido, he uses the same style the entire time but switches b/w different modes of operation. This is rarely seen even among the ability users, forget about Haki-based fighters. I am not saying Shanks can't be anything besides a swordsman, but so far nothing but fan assumptions suggest he is anything more than a swordsman. The arguments usually go like this, "Kizaru can fight with a sword when he's a DF user so Shanks must not be a swordsman too." The thing is, the rationale we use for Kizaru doesn't apply to Shanks because he's nothing like Kizaru. I have yet to see someone point out some kind of attribute about Shanks that prevents him from primarily being a swordsman.
Again, it's possible Shanks is not primarily a swordsman, but there is ample evidence suggesting he is one while there is none suggesting he is not one besides the people's obvious lack of interest in admitting Mihawk could be that strong.