Is he really? That's debatable.
But that's the thing, there's no right or wrong answer. It's all our own opinions. It's very interesting to discuss this from all points of view.
The downfall timeline is the most plausible.
Do you seriously think a boy with a swordwould be capable to kill a demon monster from the depths of hell (Ganon) that only knows one thing, how to kill. Link would be slaughtered by the monster or if lucky escape with his life.
The Adult timeline...