Wan was banished for for starting a rebellion and not revealing who was involved, since the Chu family hogged up a majority of their cities food and Wan and his friends had to live off of scraps and whatever food they could get away with stealing.
Wan did learn firebending from the dragons, you an see him clear as day doing it.
What im saying are not assumptions, bending still remained a martial art in tlok with new styles developing over the years (you have no proof it even stops as plenty of characters such as Tenzin, Korra, Jinora, Kya, Unalaq, P'li, Tonraq, Mako, Bolin all utilize traditional forms of bending, with Mako and Bolin utilizing probending styles due to their background, and Korra utilizing both styles).
Bending didnt exist during Wans time, hell the word bending wasnt even a thing as not ONCE in either beginnings episodes is the word bending used at all as it is in the. Whenever the humans left their lion turtle cities to gather food and such, the lion turtles would grant them quote "the POWER of the elements". Again just because you can throw a punch or kick doesnt mean you're a boxer or a martial artist, there are different types of techniques and movements within both that need to learned and utilized extensively. Bending is the exact same way, people in Wans just either threw balls of fire like in super smash bros or whatever, or they just did regular fireblasts or streams like Heatblast from Ben 10 or Pyro, Ghostrider, or the Humantorch from Marvel comics, they all utilize fire in a similar fashion to how people in Wans time used the elements, do we call them firebenders no because they don't utilize the techniques Wan, Korra, Iroh, Zuko, and Azula use. Same thing with Magneto, he controls metal do we call him a metalbender? No we don't because he isnt one.
The animals and moon didnt need the lion turtles to teach them how to bend, nor did the lion turtles grant humanity the power of the elements. The moon utilizes waterbending to create the tides and such, Toph herself explicitly states that badger moles use earthbending to help interact with the world, the sky bison are able to fly because they use airbending through the use of their tails.
Again bro, tlok didnt retcon anything, the lion turtles gave humanity the elements, but the animals and moon are what taught humanity how to bend, the lion turtle gave Wan the power of fire, but Wans TEACHER was the dragon, both are explicitly and clearly shown as is in the beginnings, and backed up by Katara in the first episode of ATLA book 1, and Toph in book 3. This isnt a hard concept to grasp, nor does it again retcon anything in atla.
You're really trying very hard to hate on the show, but you have yet to back up anything you've said bro. Nothing was retconed, nor did it destroy the original cast.
Again bro, you're just hating, it's not crap nor did I entangle myself, both myself and Bryke are clear as day with this stuff.