I felt the same as well. There is a lot of plot device being introduce but not being properly explained that the ending felt incomplete. Would love to read the extras that explain about Kintia's journey to become god and others that you have mentioned as well.
from my understanding, I think having a fake god is equivalent to that law of causality, yk the novel is written by an author(god) and when it ends, god disappeared. And like the story of the lilith? i think maybe they just want people to be centred and work tgt since they all will be kinda like a zombie. I still am confuse and my brain is making up things.
I have a theory that maybe Eris mother is also a transmigrated person, that would explain her behaviour since there's no external influences that could make her that unmotivated to live. Her existence is also the reason for the marquess’s acts against the imperial family.
I think for Helena, maybe yesss, if you hate someone so much you'll hate their entire family. Tormenting Eris will make her satisfied maybe
The commoner girl become the most powerful witch. I don’t think the moms backstory has anything to do with main story. And the queen used Helena because the prince cares for her
Some part just doesn’t make sense, its not so big but but why did the commoner girl was chosen to be the fake god? How does having a fake god will help them live their lives after the story end? Eris’s mother part was not relevant. Why did Queen use Helena as a paw?(to terrorise og Eris?)
I promised ive read it carefully,(re-read at that) but some parts are just questionable