Amon was a conceptual goldmine of a character, but it all fell apart when it was revealed that his motivation was entirely based off fulfilling a revenge fantasy for a father that he hated. It isn't to say that would have made a bad villain motivation, on it's own, but whether an idea works is often dependent on where you place it. The equalist regime was promised to have been a political and social conflict that tested Korra's self-centered notions of how the avatar is suppose to be a superhero that kick's bad guy asses as opposed to a peaceful arbiter for the people to keep balance.
It just tried to alter the entire momentum of the story for no reason. This entire time, Amon was building up this huge regime and taking over the city, but it was all on a false pretense. And while the Avatar had a vested interest in trying to balance the needs of the nonbenders with the benders, what investment did Korra have with Noatak's daddy issues? She didn't even find out about them until the end of the season, but think about this: aside from gaining the information that he's a bender and general human sympathy any normal person would feel, what was she supposed to feel about Tarrlok's story? Noatak's conflict with her had several degrees of seperatation to her. Noatak is really mad at Yakone, so he tries to get back at him by defeating Aang, who is dead instead he goes after Korra.
Amon was compelling because his ideals were in immediate (but very complex and interesting) conflict with Korra's duties. Noatak is just an idiot displacing his rage at his father at the wrong person with Korra being the avatar being entirely irrelevent to the situation. She has no vested interest in Noatak as a person, he's just an insane guy attacking her for no reason. If Noatak had displaced his rage at Tenzin, the entire conflict would have played out in the same basic way. It could have been literally be anyone at all. Korra's value as the avatar had been completely disregarded by the situation, which stopped the equalist conflict's momentum dead in it's tracks. The equalists just no longer mattered, so Korra's capacity as the avatar no longer mattered. Noatak's conflict would have been better served if he was just a random one off villain for an episode, or atleast as the villain of season 2 since atleast by that point, we'd have gotten to care about Korra as a person more.
It's like everytime I think of the last two seasons, I think of new ways to hate them
Yep, well said. They had the perfect villain/concept set up. In fact, Amon's motivations and actions would have made him much better than Ozai (who was just a psychopath that wanted to spread his empire and eventually be the ruler of the world). Amon represented a complex conflict that WOULD arise in a world where those with magic and those without have to coexist. Those with magic would always have the upper hand, and given human nature, class/discrimination and tensions would arise.
Prior to this, everyone was living in their own nation. So benders were more so seen as being a special asset to the tribe/nation. The benders were working for them. But once you get rid of nations and have places like Republic City where everyone has to inter-mix, benders then become their own individuals with their own drive. And at the same time, they also have other benders from other areas to group up with.
One of the reasons that Book 1 was so great early on, was because this premise was very mature and felt like the writers from ATLA were stepping up their game by tackling serious issues of equality (in ATLA, they tackled a lot of subjects, even if sometimes with subtext). This was a more obvious issue, and it was being tackled head on.
Having Amon be some random person that just wanted revenge, was a big fuck you to the entire premise. Especially since the writers decided to completely get rid of the plot once Amon fell. I agree that Amon's story with his father COULD still have been good, but ultimately they didn't have enough time to emotionally flesh his character out.