Is a good idea for Manchester United to change the manager because Erik Ten Hag was the biggest problem Manchester United was facing before bringing Amorim because if not for Amorim, we don't know where Manchester United should have been in the league position currently.
Even with Amorim, there is no serious improvement in Manchester United’s performance. Even with a new coach, their performance is not so good, Manchester United is still at the bottom of the table, so we can’t completely put blame on Ten Hag alone, the players are supposed to be blamed also. I will say Manchester United's main problem is their players, and not only the coach, because if Manchester United's problem is the coach, then they should have been in a better position, but Manchester United is still at the bottom of the table even with the new coach.
Gradually, Amorim will surely repair the team he just came in this season and he will take him times before he understands the team very well. and he will do the need full and bring some new players in the team.
If Amorim doesn’t flush out the players currently in Manchester United, then he should sign new players, otherwise, I don’t think there will be any serious improvement in Manchester United’s performance. We all can see that Amorim is a good coach, but even with that, Manchester United's performance is still not good. Amorim will just have to sign new players if he wants to improve the team's performance.
Because Rashford is not doing well in the team again and that causes why Erik Ten Hag is losing games he usually start with him and is not in a better shape.
Rashford is no longer useful at Manchester United, his performance has dropped so much, and there is no sign that he will improve, so the best thing to do is just for him to leave the club, there is no use in keeping Rashford, because he doesn’t longer perform well in Manchester United, maybe when he joins another team, there will be improvement in his performance.