I've watched a few games that he's played in La Masia because he's played in the same age group teams at Barcelona as a good American player.
I would say that Fati is going to be a good player, to some degree. Is he guaranteed to be a top 10-15 player in the world? No, he's not that type of prodigy, but I think you can say that as long as he stays on a good path, he should be able to play in a top league. From there, it's hard to predict. It'll depend on how his game develops. But he's not a fluke. He's one of the best prospects to emerge from Barcelona's academy in recent years. Then again, he's a 16 year old prospect, so you can't say whether he'll turn into a run of the mill professional footballer at Malaga or a Ballon D'Or candidate. Will he be similar to Munir or Adama or will he be the next Barca level player to emerge from La Masia? There aren't that many players at his age that you can say will definitely be Barca level.