Avatar was always lib, just that when they tried to do any complex storytelling it gets blindingly obvious. The bad guys in ATLA are largely just incredible dickheads and clearly in the wrong so they're easy to write. Zhao, Azula and Ozai are all just terrible with no real ethos other than we strong you weak. They're so clearly in the wrong.

When you try to make a villain that is meant to have some kind of point (all of them in Korra are meant to) the status quo defending and libbery gets much more obvious. Also notable that the one they bat the most for is the fascist that had wunderwaffen and concentration camps. She simply cared too much for her people.