Attacking a character for their character is fine.
Attacking produces being driven by sexism is fine.
Attacking a character because they were created by sexist producers, is sexist.
Attack the creation process, sure. But judge the character on the character.
You just attacked Harry Kim as a bad character. That's fine. It would be nice if you were more specific, but it's not important.
Your critique of 7 have been all about her appearance. (Comming up more substantive criticism of 7 now, would only seem a justification after the fact. I wouldn't recommend it.)
Another argument is: In US entertainment, nearly everyone is cast largely because of how attractive they are or aren't. Even the "uguly people" in movies, are usually just kind of average looking. Singeling out the "sexy one" for being cast by their appearance is sexist.