Eh...fair enough.
I've gone back and forth on the art direction of TLA vs LoK. On one hand, the character designs of LoK are more realistic. I think everyone noticed this when Iroh came back into the show, and everyone noted how wierd he looked next to Korra and other characters. I usually prefer the more realistic aesthetics...
However, I feel that TLA was far more expressive. I don't know if it's specifically because of their slightly more cartoony aesthetic or if this is just yet another failing that LoK brought with it or what. I also think it's because LoK is far more afraid to have 'serious' characters like Korra and Mako be the butts of jokes, which allowed more exaggerated expressions for Aang and Katara and Toph. Plus just more variety in plot situations that lent the expression of character actions that wouldn't happen most of the time. And variation in costumes are more noticable in TLA than in LoK.
Plus art direction isn't limited to characters, but also environments, and I think we can agree that TLA kicks LoK's shit in in this department. Upside down temples, a city with an interconnected rail way system, the massive library with technologically advanced solar observation system, various temples in beautiful ruin, an aztec style city, etc. And again, the fact that most of those were utilized in some way by the story lends to their coolness vs if they were just there as background decorations. Nothing LoK had is remotely as impressive.
It's hard for me to tell if I just flat out prefer TLA's aesthetics or if LoK just underutilized what it had that much. But either way, yes, LoK's character models are pretty good, generally speaking.
Yeah, well, that's what head canon is for. You can pick up some of the slack for when the writers are lacking.