Very well said. I think many of the best villains say something of value from a critical point within the story they're telling. That Black Adam description is on point- he's vigilantism taken to its fullest conclusion. I'd also argue that his rule in Khandaq offers interesting quesitons about soveriegnty, imperialism, democracy, and modernity.
I think similar breakdowns for other villains could be instructive.
Sinestro questions whether the Guardians should be trusted, and arguably fulfilled the mandate of the corps (which calls into question the notion of "order" and the purpose of the corps)
The Joker often questions whether or not good or evil is an arbitrary matter of circumstance.
Red Hood questions the rigid morality of the classic no-kill rule.
R'as Al Ghul, Poison Ivy, and others of the same type question whether superheroes are an impediment to social change.
Similarly, Lex Luthor questions whether superheroes stall humanity's development.
Zod questions whether one has a superior ethical obligation to one's own species, and how far one would go to satisfy it. (Same with Mr. Freeze and Family.)
Deathstroke questions the reader's ability to accept a murderous lack of empathy and fierce familial love coexisting
The Rogues ...are just badass