While Yakone was definitely abusive to both Tarrlok and Noatak, they weren't enemies in the strictest sense. Their characters designs as they age reflect this when he looks fifty or so and has gone gray haired, she has only put on a little weight and is otherwise still twenty-looking. Tellingly, the reason Tarrlok gave for him dying a broken old man wasn't regret for his actions, but the thought that his plans for revenge had failed. He rivals Ozai at this, possibly exceeding him when he made his two sons bloodbend each other.
He was capable of performing bloodbending at any time without the need for hand motions, and used his powers to rule Republic City's criminal underworld.
According to Tarrlok, he was such a serious threat that Aang had to deal with him decisively. A man who threatened Republic City during Avatar Aang's adulthood.
