You see the reason sora is 1st bcos she got no friends and studies so people dont make fun of her. If she gets a bf and many more friends, you know what happens bcos she isn't a slightest bit mindful about her dropping scores. I know I sound like a boomer here. Plus Jae-in is creepy, no doubt there.
Lest assume Haena is a not a good character. Now what will u say about a girl who actually admires other girl and is worried about her safety and her company when she sees she is befriending a delinquent. Ofcourse Haena is a good character here bcos we know she is. In Jae-in POV, she is a bad influence on her competitor bcos she is from a delinquent school. But Your point is valid too. NO worries.

See, jae in is right here bcos she wants sora to have a career before romance which is always the right choice. Period.