The difference between the Kira costume and Seven's was that the occupants were built differently. Therefore it can be seen as crass and sexist to have Seven in a form-fitting suit, but no one says that with Kira. Seven was an intelligent character, and well played. Voyager wasn't as good as DS9, so that doesn't help.
If everything about Nana Visitor and Kira, acting, writing, costume, etc., were just the same, but only with an endowed Kira, there would be cries of sexism against her character, too.