This post is complete BS and headcannon.
Shanks was always a swordsman but because some couldn't handle Mihawk being stronger than him and being at least Yonko level they continue to push just absurd nonsense and BS. Even after Shanks has been called a swordsman by official One Piece information they continue to claim he's not and ignore fact.
WB called Mihawk and Shanks duels legendary.
He doesn't give many compliments like that so that statement tells us those two were incredibly powerful even back then.
WB was surprised when he found out that Shanks lost an arm and wondered who could do that to Shanks. Even thought tlmMihawk might have did that to change who once again speaks volume of Shanks and Mihawk's strength.
Mihawk didn't take Vista serious. He wasn't thinking about him or focusing him for most of the fight. Compared that to Big Mom who failed to defeat Marco. She had an even clash with marco. Relied on her child's help to beat Marco. She ran away from Marco State and she didn't have enough power to wasting them.
That's pathetic. Yet, some claim that she's as strong if not stronger than Kaido.