Amorim's departure won't make any significant change in the club, he joined mid season and was yet to master the player's performances, he's not all that experienced with their strength and weaknesses. Sacking him due to the poor results is wrong, they need to give him another benefit to play next season, and to apply all he's understood about the club, since his emergence as the coach, and bring in fresh strikers to the team. Then, if nothing remarkable happens they can take up another manager. Man U has been facing managerial problems since the absence of Sir Alex Ferguson, switching from one coach to another won't help the club.
Agreed about this sacking Ruben Amorim is not going to have any impact on Manchester United performance management needed to be done better and wise decisions because they have already done enough damage which bring this elite club into big miserable soccer club. He is doing his work with he also needed time for having things on his way this is not easy because he joined this club in mid-season and things were not good even now going more problematic, but overhaul can bring positive changes.
Their recent defeat against Fulham in FA Cup bring more setback, but things are surely had enough space for fighting back into coming season while more players will be offloaded which fail to give their best here.