High Level Techniques of Bending in ATLA progresstion to TLOK.
If you’ve noticed, only a few people in ATLA could perform the high level subsets of bending; Lightning (Azula, Ozai, and Iroh), Metalbending (Toph), and Bloodbending (Katara and Hama). In TLOK, it seems like a lot of people can perform these and it has become more common. It’s quite realistic actually. Back then, only rich people can afford education. As time goes on, modernization required more people who could read and write which would give you jobs, obviously their someone had to teach them how to read and write until it became more common.
With bending, the power plant required firebenders to learn lightning. Someone had to teach them how to create lightning. Toph started out with her metalbending school then establishing her police force (btw I revised the text in Toph’s gif). I doubt Katara taught anyone how to bloodbend, since she is against it herself (I do believe she gave Korra basic information about it). Waterbenders like Tarrlok and Yakone probably figured out a way to bloodbend without the help of the full moon (They were probably part of the Red Monsoons)
I think that benders in TLOK are more skilled than benders in ATLA, but benders in ATLA are more powerful. The benders in ATLA took time to be masters, but they were able to create huge waves, powerful earthquakes, and lightning that could kill you. In TLOK, Mako’s lightning seems to be weaker than Azula’s, which can hurt you but not enough to kill you (Though Bloodbending is another story) Another reason why bending seems to be weaker in TLOK is the war is over, they don’t really need to learn bending to survive compared in ATLA. Now Bending is used for other stuff, like jobs (Pro-Bending Athletes) This gives benders an advantage over non-benders obviously. Mako and Bolin are not exactly masters, but they’re able to get by in the city because of pro-bending.
Just my two cents :D