Political commentary doesn't make a show more or less relevant. What if people are tired of political commentary to deem it relevant?!! Maybe they seen it a thousand times, or maybe it is hard to relate to in a personal level, since it deals with abstract political, and philosophical concepts at any case i find it to be a subjective notion. For one, how do you define what means to be relevant exactly in this case? from what perspective? What it means actually? Only then you can say if it was relevant or not. Usually it is history, or time that answer that question, not critics. And looking back to the track record of both shows, i do think Last air bender was much more impactful to the audiences. Generally speaking.
It is much more engaging and relatable to read, to watch, something about inner conflict, or as William Faulkner puts it - “The only thing worth writing about is the human heart in conflict with itself”. It can be within a political commentary setting, or not. Just because a show tackles Politics doesn't automatically make it relevant. imo.
The truth is if Korra had focused more on inner personal conflicts, the show would be much more relevant then it is right now. Because i find everything else is just dressing for the real meat in the bones.