Otobe has gap moe Tomboy-hitting-puberty energy.
Hebikawa has that bad girl "I can fix her" with a complex backstory.
both are going to attract more fan attention than our main girl who is socially awkward but in a realistic and not a adorable girl-failure one.
And in both their cases their primary narrative conflicts directly related and bring them into.... "opposition" might be the wrong word, but they have narrative conflicts that Keisuke is a key component of, so they have more dynamic interactions with him.
Kusunoki is a absolute cutie cinnabon bun but in addition to clearly being the fated winner, but as stated above she's just sort of awkward. If she was a girl-failure with over the top events she'd probably be more well liked, but all of her conflicts are very normal and, imho, have some of the best resolutions... but they are very comfortable instead of dramatic.
To your point, she's supposed to be bad at communicating but the minute she does communicate everything gets neatly resolved, and she hasn't had to rely on Keisuke for moral support for at least a whole volume at this point.
Its almost like there are two separate manga; Kusunoki is having a comfortable highschool debut SoL, Keisuke is having a harem soap opera drama with a mysterious snakegirl.
The "two separate manga" bit is a nice encapsulation of how I've felt about this one for a few chapters now.
To my original point, I personally just find Kusunoki more "flat" than the other two. You put it very charitably, but as a story, her arc is very simple, whereas the other three have much more growth to accomplish if they're to reach the same end point of resolution as Kusunoki.
And she's written to be kind of "perfect" - amazing at sports, perfect grades, gets the lead role of her first play and executes it flawlessly, and makes friends the moment she opens her mouth, even if they were standoffish toward her before.
The only conflict she has is her awkwardness, and honestly until we get the reason she regressed in middle school, it feels somewhat forced as far as narrative devices because she's so naturally talented in every facet that matters for school life that, without an explanation, her being so unconfident seems at odds with her actual ability.
Compared to the others, she's completed her story. And this chapter feels like the author realized that and needed some way to pull her back into the fold with the other three - there was no way to do that using the established characters, and so brand new ones were invented to plant the idea of romance in Kusunoki's head, so that at least Otobe could come along and pick up that ball and lure Kusunoki back toward Keisuke.
Which....almost feels like a disservice to Keisuke lol - he couldn't do it on his own with all his effort, and it took Students #13 & #22 along with the person she did the play with to even make her aware of him. But that's all an aside.
