I finally saw the movie. I did not think his performance was very good, he didn't deserve the oscar by any means. The character was also written poorly, basically she was an amalgam of 80s trans tropes. It did not come off authentic in any way for me, but instead like a charicature cis people drew up of their ideas of what being a trans woman means, based on knowing nothing. I wouldn't go so far to say only trans people should play trans people, but idk. I kind of feel a little bit that way now, esp after seeing orange is the new black. It would take a special cis actor to pull it off, and jared leto was not that person.
It think you kinda have to go through it to get it right. Hormones, rejection, fear, self-hate, rebirth, victory, peace. All of it.