If you like him/it or not, he'll be a deciding factor if Barça wins something or not. Fati on the right wing is just a place holder until Dembélé is back. Someone needs to provide width on the right or all opponents have to do is putting a wall around the box and shut down Alba on the left. An easy task for any decent team. Dembélé misses sitters, but he still is a goal-threat and hard to defend if you give him space.
Call it karma after his bad behavior when leaving Dortmund (Neymar also turned into an injury prone player after he mocked Barça the whole summer), bad attitude or something else. He wasn't always known as injury-prone. He became it when he joined Barça. You can see a change in his attitude. He became a more professional person and did what the club wanted him to do. That'S why he was so pissed after he got injured again vs Dortmund. After all Valverde was the only coach he had in his Barça career. Maybe Setién's training, tactics and way of handling talents suits him better. He is the kind of player who needs a father figure.
Not gonna predict he'll make it, but he looks determined and is much more athletic than the skinny chicken he was some time ago:
https://www.youtube.com/watch?v=OrKJxinYSRA