On your second point, it's probably how the book is written - if it's third person omniscient (aka, all points of view), then the reader sees the "whole" story as it happens. If it's a first person POV, then yes, the story is only limited to the main character's pov. I assume the book read by Eve is third person, so that's why Eve is puzzled by the changes.
but like, history is written by the winners, why would she take the book as the whole truth when it only depicts the glorious victory of one group
Oh, I gotcha - I thought you meant the book as the actual book Eve read, not as the history of what actually happened in the novel world.
I think there's a difference on how one looks at this, though - If you read something that happened (i.e. WW2, or some other horrible event), yeah, it was written by the survivor party/winners; but if it's just a story that someone wrote, then it is written the way it happened, since it's happened in the author's head, unless the author is purposefully obfuscating facts. So there's no survivors/winners, just plot, plot holes, and limits to the author's imagination.
To your point though, that Eve herself is kinda operating on a bias - she thinks Prince is an ML, so of course he's good and honorable, because that's how MLs are supposed to be. So it's not that the book was written by the winners, it's that Eve is making assumptions about how people are based on their assigned roles in the story.
ugh the crown prince is such a bitch standing on his moral highground "i consider you my brother" while acting like a green tea bitch and siding with his brother's oppressors
also i never get how the reincarnated fls never consider the fact that the book isn't the whole truth of the story, i mean, who wrote the story and from who's perspective, bc from what we've seen so far, it's definitely from the crown prince's