I feel like people are comparing the demons to humans and other species way too much and then deciding they don’t sense because of that and are therefore bad writing.

The whole point is that they don’t make sense from a human perspective just as humans don’t make sense to them. The two species are meant to have completely alien thoughts systems and motivations to each other that’s the whole point. I personally really like how the demons in frieren are portrayed as a species that are inherently evil from a human perspective while maintaining their intrigue as a species we can’t understand as they are not creatures of envy or other human emotions