I think sluts exist, and I apply this to both men and women. And I think that outfits that make you look like a hooker are slutty, but you're right, in this case it IS somewhat excessive to describe it (high society escorts are more understated anyway, I'm told).
It's more like, having everything gape open all over the place comes across as unattractively desperate and attention seeking. I'm not at all asking anyone to wear a burqa, but sexy is a subtle art which involves more teasing and less revealing. This is why, in my opinion, the saree is one of the sexiest things a woman can wear because a saree worn well serves two functions: concealing as much of you as possible while wanting to make a man unwrap you like a gift...slowly.