@Grahav -
It's easy to see Koto and Uchi as being caricatured to a point where it's really a problem, and I don't think it's a coincidence that breaking those caricatures has been the subject matter of this and the previous chapters. What is interesting is that the two characters are united in being the examples of romantic obsessive love focused on the Kuroki kids.
Yuu has not been flanderized. She has actually been complexly portrayed up through the present. In the entrance exam study session chapter, we find out that she is painfully aware how far Tomoko has gone forward past her, and she knows why. Yuu's apparent ease in dealing with society is limited to how well she has gotten along and how carefully she has fit her sexuality and unimpressive intelligence into it, and what she really wants is the intimacy with her friends she had in the misfit times. She can still hang out with Koto, but the chapter shows that as fundamentally decent a person Koto is, she's crazier than any of the rest. Tomoko needed Yuu as someone who lacked what Yuu had, and Yuu was open to that. Yuu needs Tomoko as someone who has what Yuu lacks, and Tomoko has not been there to catch the ball.
That's sad, but it's TRUE. People leaving behind friends for new friends from middle school through high school is the rule, not the exception. If they get to be friends again, it's because BOTH of their circumstances have changed to where they have use of each other's friendship again. Tomoko is probably only vaguely conscious of the fact that Yuu is trailing behind her; she was certainly not sensitive to Yuu's plight during the study session chapter.
My prediction is that Tomoko will be unable to join her new friends in college and will end up with...Yuu and Koto.