I'm gonna call this one, but Hiroshi was too docile for a prisoner who was once a twisted mastermind. He was obsessed with eradicating bending and very much got consumed by his own hatred. Three years later, he's unrealistically sane. I thought that Hiroshi would be in a more unstable mind to the point where he would only mutter a few words at a time. Why? Because from what I've seen, the length of time spent in prison usually take a toll on people of the same character as Hiroshi. Basically, the failure of a power hungry or anger driven villain to achieve his goals, only to end up in jail, plus the memories that led to his path to darkness, plus being trapped in prison is more than enough to make such a villain lose his sanity. I mean sure, for some people, prison does change them for the better, but for a person like Hiroshi, he doesn't fit that bill. His sanity and docile behavior just doesn't add up.
Besides, it would've been more dramatic if Asami met her father, in an incoherent state, only for her to talk him down for all the bad things he had done. Then later, would Asami realize that he's suffered enough and then try to forgive him.