While the Tarlock subplot seemed like just a subplot, I think it was just there for Sokka to make this point: bending is not as simple as water/fire/earth/air anymore. Maybe you're right, Amon is a bender, but it seems he has mastered the avatar's ability to take away people's bending, but HOW he did so is the ultimate question. I'm going to guess spiritual awakening since Aang (as far as we know) was never able to take away people's bending without the Avatar State.
OOOOOOOOHHHHH MYYYYY GOOOOOOOD NEW IDEA:
Amon said spirits told him to use his power for a revolution, maybe he was talking to Wan Shi Tong! The Spirit Owl that got violent when he found out his knowledge was being used for war? He’s sure to know what energy bending is and how to use it… Look, they even look alike