I agree, but at the same time, I found myself still utterly enthralled with the world and how it was changing. Plus, I found that while ATLA certainly dealt with some heavy topics, Korra hit some very dark stuff for a cartoon. And the creators handled those things with grace.
Seasons 3 and 4 were both amazing, in my opinion.
I can see why it would certainly peek a greater interest especially for a more older audience, though sadly while LOK had some very intriguing premises, it fell rather flat with what it wanted to deliver; everything from social unrest to depiction of fascism. Though this is mainly due to each consecutive season having a different narrative arc, and a 12 episode format is not enough to warrant enough screen time for the creators to convey everything they wanted.
However, what I do appreciate LOK for is its portrayal on race, gender and sexual identity and how the show breaks boundaries when it comes to shows primarily oriented for kids. Top notch on those aspects and others should take note as well, or would be great if they did.