I agree that Frieren villains are unique, to emphasize some other points:

• Demons are depicted as this alien species that works on a completely different set of rules: Their fake emotions seem to have evolved genetically into them and they are incapable of changing their nature. They are to humans what Wolfs are to Sheep -- Alpha Predators.
  • Also demon-kinds social hierarchy being based on Magical power level is interesting completely going against Frieren hiding her power level.

But in a way Demon mirror Frieren as well, as she herself mentally diverged from humanity over 1000s of years.

The villains in Frieren are quite similar to Dragonball villains who are non human mos of the time. During combat they find out about their similarity to the heroes.