Ruben Amorim is a coach who has good potential and may be promising in the future, but as a young manager he came to Man United at the less ideal time because I think he did not get full support from his boss, especially from the financial side. So, to be able to make Man United even better, Amorim cannot do it in a short time, and what makes it even more difficult is that the burden of being a Man United coach is very big, so there may be some who are impatient in the process, and the biggest obstacle is that the Glazers are still the rulers of Man United.
If we consider the performance of Man United in the last season, I'm not really sure about the potential of Amorim to improve Man United. Moreover, I see there is no effort to rebuild the defense line. Amorim only focuses to improve the attacking line by buying 3 over price players (Cunha, Mbeumo, Sesko). If you said there is no good support from Man United boss, Amorim couldn't buy those 3 new attackers. I think it is not about the support from Man United boss, it is about the preference of Amorim to rebuild which line.
He is expected to strengthen the defense line, but he used the funds to rebuild the attacking line. So, I can understand that many people who become impatient with Amorim because he makes an unexpected way to build Man United team.