Anakin absolutely fulfilled the prophecy. By the end of Episode 3, there were 2 Jedi and 2 Sith. Balance had been brought to the Force. The point of episodes 1–3 were to show how completely arrogant and out of touch the Jedi were, and their interpretation of the prophecy showed that. In their mind, “balance to the Force” meant “no more dark side”, which is absolutely *not* balanced for a concept with such a yin/yang philosophy.
Furthermore, Obi Wan is no “True Hero”, functionally, he’s the reason for Anakin’s fall. He raised Anakin as more of a brother than a student and was a poor teacher in telling Anakin to constantly suppress his feelings rather than addressing and confronting them. This is something that wouldn’t have happened under Qui Gon’s tutelage.
The Obi Wan we get in Episode 4 is older, wiser, and has been left alone in the desert to confront his mistakes. His final fight against Vader was his atonement for his sins. He never went into that fight planning to win.