"It's like, DC sets up these plots that almost hinge on exploring moral ambiguity and shades of gray... and then they get scared, make everyone either really good or really evil, and throw in a giant monster fight at the end."
Hm. I didn't see the Ancient League as being painted as hedonistic sadists. Tezumak and (won't name because of spoiler) are the only ones presented as really monstrous. Manitou's pretty much the good guy of the team (remember where he and Dawn wind up in the end), and the rest actually are presented as just having a different moral compass (especially when it comes to collateral damage)...and two unpleasant associates.
(The recent JSA Magog/Gog mega-arc, on the other hand, fits your description to a T.)