Ozai is like Hideki Tojo I’d say. He was ruthless and willing to do anything for power. Tojo called for a strike on the US like Ozai burned the Earth Kingdom down. So he’s realistic but as a villain he has not much more than power hungry. Azula is the best villain.
Avatar's villians were waaay better than Korra's, mostly because the way Korra dealt with the villians was uninteresting, (Kuvira was sooo stereotypical. Huge mech? really?)