Interesting idea with the swapping. Reading some of the comments below I see you mention the game spawning enemies if you don't spawn any so I get what was happening when I played. And I think there was also a effect of killing enemies too close when you become the demon lord?
There does feel like there is a imbalance with you being able to weaken the witch and then get rid of her easier as the demon lord side. It is much harder to get a win as the witch but more rewarding which was nice.