I think with United you’ll find that the coaches who were brought into implement their particular system were the ones who failed the most (rangnick and Amorim)
I don’t think Amorim is a bad manager. Infact far from it. His problem is that he refuses to adapt. That tendency does tend to be not that big a factor if the club goes all in with the manager and supports him reasonably well.
United got Amorim into the team with a full motley crew of players brought under various managers. Those players are difficult to shift out. Forget bringing in the new players.
Managing this United team is very difficult. More so for a young manager. We’ve seen it before with villas boas as well (to a much lesser extent).
The club is rotten from the ground up. It needs a complete overhaul from the academy to the scouting apart from the first team.
I do think Amorim will get some sort of a coherent system happening. United do seem to pick themselves up for the bigger teams. Whether that will be enough to save him is another matter. But at this point , he’s looking burned out 3 games into the new season and that can’t be good for him.