I'm not here to defend, because you do have some valid points here.
I just want to clarify something about the adult Cyrene a bit.
In my opinion, the adult Cyrene is actually our Mem, and not the Cyrene of Phainon's past.
Let me clarify it more. In my understanding, the Cyrene in Phainon cycle is part of data made to progress IronTomb birth, similar to the people in Amphorius and Chrysos Heir, a data part of the simulated world of Amphorius.
While the adult Cyrene (from my understanding of Herta's explanation), is actually the heart of IronTomb or the Demiurge that changes its form from just a cube that represents IronTomb's heart then changes its form over time and takes the form of Cyrene because since the beginning the only thing she knows and learn is Cyrene and the story that she told to Demiurge.
And when she escaped from the cage made by Zandar, she turned into a fairy form of Mem (because she drained almost all of her to escape), thus became the Memosprite of our TB because Mem are in sync with the Stelaron inside our TB. But in the process of escaping the cage, she also loses a big chunk of her memories. Meaning, meeting TB became her new start in her memory. And this might also be why she seems so attached to TB.
Now here's where I want to clarify even more that the Cyrene, and the adult Cyrene/Demiurge, is the same person yet different.
Like what I explained about the Cyrene from Phainon cycle, she is a data, while Mem/adult Cyrene is Demiurge, that's why I say that they are not the same person. But at the same time, a the same person.
(I know you might be confused right now, but hear me out okay 😅)
At the beginning, the heart of IronTomb/Demiurge seems to be in a state of blank, it doesn't have a consciousness of its own, it doesn't have feelings, it's all blank.
Then came Cyrene. Telling the story of epics and inserting data into it in the hope of doing something to prevent the progress of IronTomb's birth.
And that's where the Demiurge starts to learn. Learn to understand, learn emotions, learn to have empathy, learn to love,
She is taking the form of the adult Cyrene because the Peach she loves so dearly doesn't get the chance to grow up. (From what I take, the Cyrene actually yearns to grow up. She wishes she could grow up to be an adult, but she can't/didn't get the chance to)
From what I learned, Cyrene, is actually gone. Like, disappear or the data is obliterated, delete. The only thing that remains is the memory of her, which I believe Mem absorbed. So in a way, the Cyrene and the Mem Cyrene became one. She has the memory of the Cyrene from the cycle, but she also still our Mem.
And since Mem got all her memory back, combined with the memory of Cyrene, she became the Demiurge we all know now.
That is all I can say about it. In my opinion, Cyrene's character has ups and downs in the story. I do not dislike or hate her, but I can also say she isn't my favorite.
I also understand why some people dislike her, or hate her. They have a valid reason of their own.
I just made this reply to say my own opinion on Cyrene.
And by all means, I never claimed to be lore expert of HSR, all this long a*s paragraph is just my opinion and understanding of the 3.7 patch story ( ̄ ▽  ̄;)