At the risk of casting judgement too soon, I'll say this.
In my opinion, almost all of our previous failed managers showed very quickly that they were never going to succeed, aka win the PL and/or CL. We've come 2nd before. We've won the FA Cup and League Cup. Europa League. All the minor trophies. Those were not considered successes. Success at this club is an extremely high bar.
The people that pointed it out early on were of course talked down. It's not the done thing in Man Utd support to cast negative judgement on the manager too soon. Unfortunately, in the end they were proven right. And more painfully, we wasted years, billions of pounds, and loads of talented careers to find out the obvious.
As with Amorim it's early days, but he is showing similar signs.
With managers though, it is different. It is all about decision making.
It's possible for Amorim to completely turn this moment around, but not with the route he's going. He needs to re-evaluate his strategy, because he's clearly a talented coach but he is making a lot of obviously wrong decisions thus far (possible due to age/inexperience) and if he does not course correct, he will fail.