The author didn't seem ready for a second run but rather had a vague idea of what he would like, which wouldn't have filled the pages he needed to so they've just thrown in what they can to extend the season.
Yuri doesn't delve into this territory much but this is par for the course when it come to shoujo series that continue past confession. I want to say it'll get better but if you came for fluff this really isn't the series for you.
Anyway, at least we got to hear Kase's reasoning but she's still a fucking dumbass who can't seem to comprehend there's consequences to her actions. Yamada needs to slap her upside the head but she won't; seems like she's trying to make sense of it and at least confronting Kase about Fukami to some degree.
The author is a woman. I still agree with your points, though.
I have noticed this so much when it comes to stories where the characters finally get together: no plan from the author.
Either they break up, or their relationship is now a series of misunderstandings to keep it interesting. Normal, angst free relationships aren't considered interesting to readers, so the writer is trying to spice it up.
But also, I think Kase-san had a good thing going. The first series had them together and the misunderstandings made sense. It's only with this series, that it feels like the author has no plan.