Well, I agree with some aspects of the argument you’re making. If the driving force in Korra’s characterization was a love triangle, then that would definitely be confirming bad stereotypes.
However we have quite a lot of information that so much of her story is going to be focused on her emotional and spiritual struggles with bending and trying to stop the anti-bender revolt. Korra has a lot going for her, so even if she is involved with a love triangle it won’t be the basis of her character.