Zenyatta is much more reliant on precise shots. Unlike Genji, Hanzo, and Junkrat, he has no backup plan if his projectiles are missing. He either makes his shots or he dies. And yes, that 1 extra shot makes a huge difference when the person coming at him is Reaper, McCree, Torbjorn, or you know, every single character that is not Tracer. Reaper especially, since the 50 HP barely makes a difference to him.
He's a better support and a much more viable pick. But he's worse at the one thing he used to do well, which is a little displeasing.