It's so weird that people are like "Pavi and Nisha mastered all 4 elements! They're Mary Sues!" Like no bitch, they're bending the elements, it doesn't mean they mastered shit. Even Aang by the end of book 3 was told by Toph "Your Earthbending still needs work" and he was doing this shit:
static.klipy.com
Aang Earthbending in Ba Sing Se
ALT: Aang Earthbending in Ba Sing Se