You make a good point, I'm still not sold on Hebikawa and Kusunoki switching roles but one thing I should say is that Kusunoki is not flawless, she's already got a few problems and she's aware of those.
One thing I would like to see is Kusunoki and Moe ambically solve their mutually shared feelings for Keisuke without harming their friendship, it helps Kusunoki get over her previous trauma and it gives another reason for Hebikawa to start changing.
No, I'd argue Kusunoki is flawless, because there's no inherent part of her character that stands in the way of her narrative goals at this time. Hebikawa has an obvious flaw, and even Otobe has her abrasive/tsun-ish personality that prevents her from being honest about her feelings toward Keisuke (and we even see it come into play aganist Hebikawa, and also in this chapter when the random classmate asks her and Kusunoki about crushes—so it's not just blunt wording and aggressive mannerisms towards the target of her affection, but basically every character who isn't Kusunoki).
But Kusunoki has resolved every challenge in front of her with surprisingly minimal effort due to her natural talent, which is a consequence of the way she was written. She's academically gifted, she's athletically untouchable, and even in sociability, she stole the show during the theater performance back in the festival arc and managed to win over even her detractors among her classmates by "just so happening" to have both the cultural knowledge and the savvy to speak directly to them about things they found interesting or important. She can even talk to boys now, in the absence of Keisuke, as evidenced by the train scene in this chapter, and that's just being depicted as something that's happened off-screen because there was never any moment in the actual storyline where we see it addressed and resolved.
The only "big thing" she has is the aftermath of that traumatic incident of hers from sixth grade, but that's not an inherent facet of her character, and she's shown throughout the series that she could easily resolve it the moment she applies herself, just like she's easily solved every perdicament the moment she applies herself before. It's also a simple matter of communication, which is something she's shown she can do proficiently, and talking with Keisuke and Otobe would resolve things almost immediately. I'd even argue that if it
were resolved amicably between Kusunoki and Otobe in that moment, then it would just reinforce Kusunoki's flawless nature, because even her "big narrative trauma", for all its supposed weight in the story, wouldn't amount to much if it could be fixed with a conversation and everything was all smiles in the end. After all, Otobe is deferential to Kusunoki first and foremost. She'd bow out of the way at the first sign of actual friction, and it would result in her having to effectively shut down her feelings for Keisuke in order to keep Kusunoki as a friend, which she would do only because she's been a set up as Kusunoki's friend. There's no agency for her in that instance, unless an actual confrontation were allowed to happen that saw them push against one another before finding a solution that (hopefully) allows them to remain in one another's lives.
Thus, what would be
more interesting, in my book, is if she actually wasn't able to immediately resolve it, because she started feeling jealous of Otobe and how close Otobe was getting to Keisuke. It pushes Kusunoki toward that "darkness", which would give her something meaningful to fight against in order to resolve her past trauma that would give real weight to the accomplishment. Everything's been quite easy for her, up to this point, and the anxiety she feels is something that could naturally turn ugly. I personally think it would be a more compelling story if she really did start to "fall", and needed help to pull out of it.
And I would argue that would dovetail perfectly with Hebikawa changing as has been portrayed, because she's also an integral part of the series both as a romantic foil for Kusunonki but also as her mirror/"dark" iteration. Kusunoki and Keisuke inadvertently working together to help pull Hebikawa away from her old worldview would set her up to turn around and use her newfound perspective and healthy mindset to prevent Kusunoki from sinking down to where Hebikawa herself once was.
That would also satisfy Hebikawa's arc and resolve it, because she would have the perfect chance to gloat at Kusunoki's darkness being exposed, and instead she would seek to help save her in the same way she was, herself.
I'll say that this is all if
I were an editor of the series with a say in its direction. I think it would effectively tie each important character into the story arc of the others, and force them to confront themselves in a meaningful way while resolving the underlying themes of mirroring and growth that are present in each of their characters. I don't know if the author will go that direction, of course, but it would be nice to see another side of each character that shows they've more depth than we've had depicted up to now.