Yes, that demon is literally a concept of Evil given physical form

Even then, in my worlds I still occasionally like to include the edge cases of outsiders rejecting the evil of their archfiends (or overlords, what have you) and, if not redeeming themselves, sometimes being a little bit more chill (sometimes still morally dubious but in a more fun way).

I think my tendency towards a historical materialist lens has really affected my worldbuilding lol. I always like to logic out how outsider societies would work in my settings given such concepts as soul-corruption, damnation, souls as currency, immortality, and on and on. I find it much more interesting that way.

Yeah a fiend society and most fiends are "evil" in a similar way to any of the truly evil empires in our world and their supporting people are - with the added fun factors that a large percent of the population may literally be harvesting damned souls, or be born from the greed/hate/lust/jealousy of former mortal souls. I like a demon not having to be 110% inevitably bound by their origin