Boa still has cropped straight sidelocks. And that's the main thing about hime cuts: they're cropped straight. They're meant to look prim and proper, are heavily associated with high class and proper characters, and are high maintenance, implicitly demonstrating a character's high levels of discipline. They're also strongly associated with lolita fashion, hence Mirai having one.
For one thing, from a character standpoint, someone like Asuka or Katsuragi having that sort of hairstyle makes no sense. Both of them are hot-blooded types who forego elegance in many things, including speech, battle, and dress. Neither of them would spend the time necessary to keep a hairstyle like that. This is important because in a lot of things, a character's hair is used as a shorthand for their personalities, and SK is no exception. Hibari and Minori have pigtails that emphasize their youthful energy, Yozakura's hair is kept short for practicality's sake, having grown up taking care of numerous siblings, Murasaki has super long hair because she never leaves her room to cut it...
Secondly, like I said, the hairstyle is meant to look proper, being that it was used by nobility. Asuka's hair, while not necessarily unkempt, is very casual and shown in such a way that she doesn't seem to pay super close attention to how it's styled, with some strands just kind of flaring outward any which way. This goes against the entire point of a hime cut from the start, which makes sense, since Asuka is not at all a formal or proper person; she's very casual and friendly. Not to mention every single part of her hair seems to be a slightly different length, which is, y'know, not a hime cut.
tl;dr saying Asuka has a hime cut is like calling a mango an orange.