... is there really a subset of people that consider Korra a Mary Sue because she took to bending other than water so easily?

Aang was trained as an airbender and the idea of the avatar was so mystical that he wouldn't even TRY bending anything other than water but the moment he accepted his role as the avatar, he literally took to water and fire bending just from watching others train.

Korra, in a world where the avatar literally saved the fuggin' world from the fire nation, would've been told stories about the existence and possibility that anyone can be the avatar and... I dunno, experiment in a multicultural bending world even at a young age.

Hell, that's how they found out she WAS the avatar - not a child's game they used to determine Aang was the avatar by having him choose toys.

Different circumstances.

Secondly, Aang learned earth-bending in, like, a day while it took Korra weeks to learn airbending - don't see how it's BS'ed when literally Aang just had to save Sokka from a rampaging moose-lion in a day or two.

Korra had to struggle to learn air bending and, in the end, didn't even become proficient in it in any spectacular way until, what? Chapter 4 facing the convict that learned air-bending after the spirit convergence?

"Korra didn't train"

So I guess a decade plus training with the White Lotus to learn Earth and Fire bending separated from her family and tribe in such a way that she had a major disconnect with them wasn't training.

Jesus.

Let's forget that, I dunno, BEING the avatar gives you a connection to the spirit world.

Imagine actually being TOLD you're the avatar at, like, 4 years old & moving onward versus being a member of a nomadic culture and not told until 12 years old - and not accepting it.

Every bit of delay in Aang's training can literally be whittled down to the fact that dude straight up DIDN'T accept being the avatar.

He ran away from it.

Compare that to a more open, more multicultural search for the avatar that would have water-benders searching for and pining for the next avatar - yeah, I can see water bending parents telling their kids they could BE the next avatar.

So a 4 y.o. experimenting with bending?

Kiiiiinda fucking plausible in this new, post fire-nation terrorist world.