P.Y., when Reb Moshe referred to the “derech all women dress in the city”, he is referring to frum yidden, not goyim.
People tend to notice and have hirhurim from their own kind, i.e. other yidden, much more than from goyim. Sure goyim these days dress literally like chazeirim on two feet. But when frum girls dress provocatively they cause other yidden to sin. Unquestionably.