Coaching Man United is not easy, just look at how many coaches have been fired by Man United. Because coaching Man United has pressure because this is a big club, big history, the biggest fans in the world. Consciously or unconsciously, the scary job is to be the coach of Man United for now, because failing to coach Man United, a career as a coach will also fade. Amorim took this step of course there has been quite mature consideration, and to judge Amorim's performance is still too early in my opinion. So it is not wrong if the club management gives him a season.
In essence, the key to success in coaching Man United like the Sir Alex era is because he also acts like a club owner. This is as conveyed by Rio Ferdinand on his Youtube channel, he said when he was still a player, if Man United players were on holiday from training, Sir Alex was still present in the work room to control and supervise other departments. Players who performed poorly in the first half were not invited to compromise and were immediately punished in the locker room in the middle of the match, if they were still stubborn they would definitely be sold. Maybe Amorim needs a firm stance to fix the club and of course give him the freedom to buy players. Because believe me, firing the coach is not the solution, management should understand this.
You are right. The club has been experiencing poor performance since the departure of Sir Alex Ferguson. The coaches should not be solely blamed as Ferguson was able to be successful at the club due to the fact that he had significant control in the club. In my opinion, Manchester United will continue to see coaches come and go without long term success if they don’t fix their internal problems.