Amorim needs time to get the current Manchester United squad to be prepared for the rest of the season. We shouldn't use the impact that Ruud got to expect same thing from Amorim. The players knew that their position weren't guaranteed with Ruud therefore they played very well to try and get more playing time but under the new permanent manager, after some players get it that they're part of the first team, they won't be overplaying again but to reserve their strength for other games therefore we mightn't be getting the same energy we use to get from them and it can affect the teams performance therefore it depends on how the manager handle the situation.
Ruben Amorim of a truth will need time to introduce his own tactical approaches to the team but don't think it'll take him too long to do that. I listened a recent interview where Manchester United manager Ruben Amorim said that one thing you must expect from his Manchester United team is they'll play with their own unique identity and that I think is one of the things that's been lacking at the club since Sir Alex Ferguson retired as their coach. The team doesn't have a style of their own which is why it's been difficult to succeed since then but if Ruben Amorim can successfully achieve what he said, I think it'll be a good direction to significantly improving the performance of the Manchester United team.