Just like when he first set foot in Sporting he also did not know the players in the team and it took him at least a few seasons until finally Sporting's performance improved from year to year, it is very unfortunate that Amorim had to leave the club when he loved it and chose a club that was in chaos and he was forced to build the club from the bottom, I think we need to give Amorim time because changing a club in an instant is not the job of a coach but the job of a magician 
Amorim is a business man, and wants to show his skills and experience to the world that he knows how to revive a club that's is stumbling. He did it in Sporting and can also do it in United, if he gets his desired players. Amorim is still young and has more talent in him, he needs more time to transform the team and we can start seeing good results from next season. After all, you could get bad results without spending much money neither, and that is why I believe they are looking like they need to stop spending that much money. They already have hard time keeping Garnacho and Mainoo who they should keep, both of them are great young talent that could do amazingly so we should consider how they could help them in the future, spend money on those players to keep them.