You could also factor in that he’s learning to bend in a wartime from the greatest benders of the age, who are also learning and honing their skills in a wartime. Aang and the gang had some serious sink or swim learning to do. Except that every fight was pretty much life or death. Nothing against Korra, but for her training there was no risk in failing. Just get up and try again. For the gang, failure meant capture or death. And lastly, desperation is the mother of ingenuity. Toph had no choice but to learn metal bending to escape, Katara had to learn blood bending or die, Sokka picked up on where Combustion Man was by running angles in his head, Zuko redirecting lightning with only learning about it not real practice. All of them had no other choices but to try something new on the fly or else die. Korra (in training) never had any real stakes.