Demons in frieren aren't evolutionarily correct

In frieren, demons are these creatures that doesn't understand even a bit of humans emotion. That being said, evolutionarily, demons who were born and can percieve even the slightest shed of emotion should be at a natural advantage to any other demons. Say the village incident, had the demon girl understand even the slightest of emotion, she'd been grown into an adult unharmed and loved. Evolutionarily speaking, having emotions and the ability to percieve them is an advantage. The thing is, they don't have emotions no matter what, which is strange, because if we were to say that demons traits are born from their mother and father, there should should a chance that a "defect" occurs, and the demon can be emotional. Those emotional demons would be at an advantage to almost any enterprise compared to the other demons. Imagine if aura actually have emotions and she has a lover, himmel can't even do a thing