I don't really know how you view it on your own perspective but as I'm concerned I think he make a very good decision by concentrating in only Europa League, he was just trying to strike a balance because he really know what they can do and that is why he need to make that decision. Amorim hasn't spend a whole complete season as a Manchester United coach so I believe it too early to call him a weak coach, I'm not a disputing your fact but at least let's give him more time to test him. As for Marcus Rashford that has left, it really a great loss for the club, but I think Amorim don't like him and that why he let go of him.
When Amorim came to Manchester United things were already rough and it will be very difficult for him to fight for the top in every competition that why he picked Europa League since they were having a good time there. I respected for make that boldly move.
Amorim took charge of Manchester United at a time when the team was completely broken. Manchester United was in a very bad state. There was no specific strategy. The bonding between the players was very weak. Amorim tried to stabilize the team gradually. But so far he could not succeed.
United tried hard for the Europa League title in the last season. Amorim's goal was to qualify for the Champions League by winning the Europa League title. But we saw that Manchester United lost despite performing well in the final match. Of course, we cannot blame Amorim completely for this.
Amorim tried. And perhaps Manchester United management will give Amorim more time. This season we can see that Manchester United is willing to rebuild their entire squad. The management is not in a hurry. They are interested in building the squad gradually. We will see positive changes at Manchester United in the next few seasons.