It's impossible to tell where Mihawk and Shanks stand unless they fight again, his title comes from his reputation of being undefeated against the swordsmen he challenged but he specifically refuses to fight Shanks (inconclusive duels) after the loss of his arm, WSS isn't a video game achievement that gets updated whenever a stronger swordsman exists but the reputation of man known for his giant sword and his victorious streak.
I can see why people feel Shanks shouldn't be weaker than Mihawk, but most reasons they use to dismiss Mihawk's claim as the WSS are invalid just like the Hakiman argument. They just use whatever dumb loophole they could come up with to say Mihawk isn't as strong as he is because they hate the guy.
Mihawk wouldn't be recognized as the WSM if there are other swordsmen who surpass his infamy. Shanks, in particular, isn't living under a rock. He's one of the most famous swordsmen in the world. And everyone their moms knows about Mihawk's rivalry with Shanks—It's literally a legend in OP world as noted by WB of all things. So if people call Mihawk the WSM, it could only mean one of two things i.e., either the world accepts that Mihawk is stronger than Shanks or Shanks is somehow not a swordsman. There is ample evidence suggesting Shanks is a swordsman while there are little to no implications of him not being one.