Well, I'm not really much of an expert, but some of the problems I noticed.
- Eleina has almost no reason to attack. Too little exp gained to top of being a Jeigan.
- Chapter 10 and Eagler are just... Wow, no part of the game should be so powerful that they negate almost all characters except one. The player has no reason to field anyone but the sage (forgot her name, sorry) on the last two chapters.
- The preceding chapters are rather easy, because of the amazing stat growths everyone gets.
I'd mention the awkwardness of Lyn's cutscenes imposed on your characters, but you obviously know that.
Good luck with the rest of the work. The story is interesting, so I'll be looking forward to it. :)