You're right, she is the most active character of all. That's why I said that she is the one putting the story in motion.It's not just her flaws that make her more interesting than Kusunoki. If she were to become a serious and mutual love interest for Keisuke with character development, she'd still be more interesting than Kusunoki because she actually does stuff. Remember the beginning of the manga when she didn't actually remember him yet? She seemed to like him at the time, we can't say that it's just "why does this guy puke when i'm with him?", she actually acted interested (read the chapters again if you don't believe me). Back then, she actually did stuff to actively pursue him. She didn't plan on keeping it to the grave like Kusunoki. She didn't give weird mixed signals like the completely stereotypical tsundere Otobe did, whom Keisuke also currently has no romantical interest in (and i don't see how he would develop it either). She does stuff. She tries. Even if Kusunoki were to start doing things now, she's still too slow, she still falls far behind Hebikawa in how much effort she puts into romantic opportunities.
Edit: Though, this may also be a bit of a matter of preference, as it depends on whether you like a FMC who confidently teases the MC or the one that is shy, but i also think that a shy FMC can be done better than Kusunoki.
She was interested in him at first because he was an anomaly, someone whe couldn't figure out. She lost interest in him the moment she realised he was someone she had already discarded (read the chapters if you don't beleive me).
She only took interest back in him to try to seduce him to force Kusunoki to have a reaction because she understood that she is in love with Keisuke. She tries to seduce him (and hilariously fails) to make her jealous and force her to show her dark side.
I can't see her winning because her role in the story is to watch Kusunoki being everything she thought was impossible to be : an honest person. As she is now, there is no way Keisuke considers her as a love interest. And like I said, the character developpement that could make her a potential love interest would be to make her become like Kusunoki. That is pointless as Keisuke has already recognised that he has feelings for her.
However, Kusunoki still has moments when she is active and pushes the story forward, like the play during the school festival. Everytime she does, she is superior to Hebikawa, simply because she a true nice girl.
People remember Hebikawa more because she is in the story to create drama, Kusunoki solves it. So yes, she is boring, but she is the healthy romantic interest of the story.
Sadly, Moe has "losing heroine" written in all caps in each scene she appears since she has fallen in love with Keisuke. Her only purpose in the story is to be a roadblock for the romance between Keisuke and Kusunoki because she doesn't want to get in the way of the romance of her friend like it happened when she was younger.