I liked this chapter a lot! I never felt much for Rebecca, but I still found this conclusion touching. I don't understand how people can see this as stretching the plot, I think the conclusion chapters are always the best part of the arc.
I didn't read through the whole thread, but I saw a lot of arguments for and against Rebecca. I don't really find her annoying, but I've come to realise how incredibly bland she is. She is mostly defined through her relationship with Kyros, and Kyros's tragic story is definitely the stronger side of their tale. I haven't paid attention to this before, but now I can't think of a single interesting personality trait that would define Rebecca. Dislikes violence? Seriously, that was mentioned in maybe two instances. Doesn't want to hurt anyone, I guess, but wasn't that mostly because her mother told her so? She has a strong desire to be with her father/the soldier, but is that really a personality trait? I would just describe her as a generic nice girl who was forced to fight. That serves the story ok, but it still doesn't make Rebecca herself very interesting.
By the way, I might have missed this in the manga or it has been discussed before, but it has been bugging me for a long time. Was it ever explained how everyone knew Rebecca was king Riku's granddaughter? Her mother "died" to the eyes of the public and she clearly wasn't Violet's daughter.