There is nothing to spoil here but just wanted to discuss what you put within the spoiler tag
It to me feels like more he is training them to be useful in his fights against evil (humans/monsters), it doesn't feel like a reform per se as he isn't making them reflect but just punishing(getting his revenge)them and ensuring he has sufficient support to fight the demon army(which, granted, doesn't seem likely with how it's shown the humans started the war).