You didn't have enough time to balance?
Characters LV limit is intended from the start, because the game is short and have no need for further exploration (after final boss is defeated). I have finished balancing the enemy, although the outcome still not balanced enough. Maybe if I develop this game again I will make the LV limit increase based on how far the story goes (assuming this game is still in "Chapter 1", LV 20 limit is enough, I think).
I will think more about this LV limits. Thanks.