^Ah, MMA. Well I wasn't far off.
I've read that the producers based Korra's look and personality on a particular athlete, a mixed martial-arts fighter or something, but I'm not sure if it's the same person they might be using as a reference model.
Anyway, the animation is definitely not rotoscoped. The animators are no doubt using live models as reference, but aren't directly tracing them or anything. So the artists' skill and attention to detail is still very much a factor.
I never said it was rotoscoped. Indeed, it's pretty obvious that it isn't. You're probably right though in that they're using the same artist for all of Korra's key animation. Or failing that they have one main guy/girl and anyone else who does it have to stick *very* close to that standard. She is after all the main character, so it shouldn't be surprising that she receives such close attention to detail.
On a totally different topic, I just stated to re-watch the show and only just now have I noticed in the credits that Tenzin is voiced my J.K. Simmons! Maybe it's because he doesn't spend the whole time shouting
, but I never would have called that just listening to him.