Stat deterioration is considered in the stat growth balance. Also, the stat deterioration doesn't start after just one day unless you only train that stat occasional. The more intently you train the stat the longer it will go without deterioration (to a point). I will consider different options for potential NG+ mode. But for now, keep in mind that the game is still being balanced. Not all items and jobs are in the game yet. And you barely have half the total amount of time to train.
Just if it's possible, make it so that on the first day you have a warning, and then you take away the skill the next day, so that I know what I need to train. I really like your game, which is why I'm asking and writing so much. I'm a huge fan of the Harry Potter universe (even if the game is just based on it)! In NG+, you could save items and spells, but you could also reset the spell levels and skills to be fair. Oh, and by the way, I understand that Mitski is a Werewolf? Her ducks are very afraid of her =)