Man I just can't get a read on the demons, and I love it. They're predators who manipulate human emotion and language, yet they seem to be capable of feeling the same emotions; they're warriors who value hard work, yet they cease to work on a magic once they consider it "completed"; they're a solo species who lack the fundamental concept of "family", yet they're also capable of working in groups to achieve a goal. What would be considered "contradictions" for a human seems to be the norm for demons, and likely vice versa.
I'd actually be okay with Frieren & co. continuing to fight them without gaining that understanding, because - unlike series where both sides are human - when there are multiple sentient species there is that very real possibility: that sometimes it's impossible to see eye-to-eye.