She has invulnerability equal to Rogue, which is where Rogue got it in the first place (she stole Carol's powers permanantly). Can you name any form of armor material that is anything close to that? Hell, that's one reason people complained about the Warbird outfit, that armor was unnecessary and redundant for someone who's natural protection was better than anything short of a full Iron Man rig.
How much skin her outfit covers is a matter of pure aesthetics, nothing more.