While being 'Darker' doesn't mean something is more mature, i.e. Clone Wars having Maul behead innocents or killing people in cartoon-ish villain reasons wasn't... 'Mature' whereas I feel that The Last Airbender often was more mature despite showing far less...

I do wonder if Korra could have benefited from a higher Parental Rating. I think Samurai Jack Season 5 largely handled its rating pretty well https://youtu.be/8eH7GeVd7-8?t=93

Princess Mononoke also had a good deal of blood and some gore/dismemberment: https://www.youtube.com/watch?v=pYDgUhzVBzE

So yeah, would Korra have improved with more leeway for violence or even more darker themes? Perhaps more suggestive romance too?