I've mentioned and showed far more than just "what happened".
Kirin definitely didn't do what she did because she's
dumb. Kirin
isn't dumb or stupid and she understands the consequences of her actions. She was literally blackmailing a friend, successfully. The whole point is them all knowing the consequences. It's also not like she needs a phd to know doing bad things to people will make them not like you. She's fully aware she's a bad person doing bad things:
Btw, Kirin should be 15 and almost 16 since Christmas is 2 months before her bday. Rin is likely the only 14 year old due to skipping ahead. Funny enough, Kirin should be older than Nodoka.
As for Nodoka, why does it matter if Yumi was changing? If you think Nodoka did this just so Yumi would get sexual with Sensei, you may have missed the part where Nodoka cucked her:
And they are even further apart from fucking now, than they were. Yumi more or less became a cockblock recently. Revenge also doesn't
need to be the sole purpose to still be a major reason why Nodoka did this to her. It's not like Nodoka has done this to anyone who hasn't traumatized and threatened to kill someone close to Nodoka.
There's also no reason for Nodoka to feel empathy or sympathy for
Yumi of all people, but Yumi knows better now, and if she'll hurt anyone, it's Nodoka, hence why she's the "Matador" and the event this happened in, was Nodoka's 'Matador' Chapter 3 Event. Nodoka made herself Yumi's target.
Frankly, considering Nodoka could fail to blackmail Yumi, and still end up assaulted if not killed, what Nodoka did was more stupid than what Kirin did.
Nodoka was being more stupid than Kirin, when it comes to blackmailing at least. Nodoka's struggle to understand others is way more of a hindrance, than Kirin just being insecure and horny, and petty in Ayane's case. Your point about stupidity being more forgivable should apply more to Nodoka than Kirin.
I do agree with your assessment of the book scene, but Futaba has literally been traumatized by Yumi and is terrified of becoming a target again:
She's not able to think rationally about the book, which is why Nodoka tried to keep her from finding out about it.
Judging her during the book scene to attempt to discredit her prior, is in poor taste, and doesn't work if one knows the context.
Nodoka's greatest priority also isn't the story, it's making everyone understand (this world), otherwise, her existence means nothing:
As she mentioned in her 'Amoeba (Incontrovertible Peculiarity)' Chapter 3 Event.
"This story" is just a popular work of hers, that she felt inspired to write. It didn't even seem intended to be read by Futaba, or the rest of the class.
She's also literally put her writing profession on temporary hiatus right now:
Nodoka has more important things to focus on.