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.
If my memory serves me right, I doubt Man UTD, in their current situation usually give new coaches time to adjust and fit into the club and I don't expect Ruben Amorim's case to be different. They saw how he helped his former club defeat Man City in the champions league and would be full of expectations for him to be able to move United back to the top four by winning games and since Amorim has been been heard saying at his unveiling that he'd do so many things with the club, I just hope he can be able to deliver and not join the long list of coaches who although have potential, can't be really show their talent just because the club's impatient.
On the one hand, there is hope that Amorim brings to Manchester United, but on the other hand, it is not really a guarantee that he will be successful with Manchester United. I think when talking about patience, management should be patient to wait for Amorim to be able to bring improvement if he has difficulties at the beginning of his coaching. Because the previous coach got a very long time to hold Manchester United.
Well, seeing all that, Manchester United should also give the same opportunity, at least until the end of the season. Let him finish this season. But with the note that he must show progress, because if it is worse then it is also dangerous.