It really feels like the author picked and chose the most important things to resolve given the situation. And I think they did a really good job of it truthfully. I understand why people are upset at the idea of resolving things in a conversation, but if there were ever a series where that was possible, it would be this one. The act of unveiling the disgusting parts one was hiding has been put forward as the way to move on and accept them, and that this is a proper path to healing. I think that's exactly what we see. And with that what needed most to be resolved is resolved, and that's absolutely an acceptable place to end a story: to not tie everything up in a neat bow, but to have a very clear focus on a part of the character's lives that the story is about, and resolve it when that conflict is resolved. Like in Niji's case, they haven't made up or figured out how they're going to move forward, but it was that conversation where they put forward what was inside that created a path toward some resolution, and that act itself, not the resolution, is what's being celebrated.
I feel very similarly. Maybe it's because I knew it was ending sooner than we might anticipate, but this felt like a qsoft landing in that context. The author prioritized the more important relationships and maintained the trajectory the series was heading towards. Megeru deciding to no longer be defined by her childhood trauma, Remu finding relationships she can honestly express herself in, and Azuki demoting her idol worship into a fun hobby are natural endpoints the series was moving towards. Like sure, I would have liked to see Megeru personally realize there's more to intimacy than physical desire, Remu come to terms with her crush on Azuki, or Azuki more clearly display a willingness to move on had Megeru not wanted to get back together, but that's how the cookie crumbled. Really Niji is the only dropped thread. I imagine she would have been softened a bit from the start with the knowledge that there wasn't going to be another volume to complete that narrative throughline. Altogether, I'm rather happy with the series and the ending though.