It essentially plays much like 5E mixed with Genesys (not surprising since so many of thevdesigners used to work st Fantasy Glight Ganes, and the Lead Dedigner of the Cosmere RPG was also the Lead Designer of FFG Star Wars: no funny dice, but some narrative mechanics). The big difference is that everything is Skill checks: the math works like 5E Skill checks, but it also applies to magic and combat.
I would add the core magic classes, the Radiants, have more in common with Jedi Knights that D&D's Vancian magic.
It's closer to Genesys (Star Wars FFG) using a d20 for skill rolls and a Fudge/Fate Die for boon or threat.
The rules really aren't tied to the Setting, that's entirely the point of whst they built here to make a cross-setting game ruleset. The prio Mistborn Adventures RPG was too closely tied between rules and setting, which would preclude mixing it with other Settings like the Stormlight Archive and others to come.
I have a theory that the people playing Avatar aren't worried about being in the TTRPG hobby. They could be playing the game with other Avatar fans without any concern for other games. Plenty of the people I played Vampire with would never, ever, participate in any other RPG. They didn't care about "the hobby." They wanted to be Vampires.
Why would Avatar RPG be appearing at TT cons then? If the interest was focused around the media, then I would expect the games to be focused on media based cons.
Because a traditional RPG publisher made the game and wants to grow it within the hobby where they are known
I was trying to find some stats independent of large cons and came across this:
