I am also quite curious why they are interested in this young player. But at least, he is considered talented, his position is only as a left-back. and at his very young age, Man United dare to take him with a fee of $5m plus add-ons. whereas for now, his market value is € 1.00m according to the transfer market data. and the reason Man Unite chose Diego Leon is because they believe that the left-back player can be a long-term asset for the strength of Man United's back line.
Yes, Amorim as a manager can see the potential that exists on Diego Leon. he wants to mold players from the beginning, and make him a great player who can be a valuable asset for the future. I certainly don't doubt him because he did it on Sporting. As we know Gyokeres are not a great player before, but after Amorim recruit him, and mold him to best attacker, then he has a high marketability right now. We can look the comparison now, Sporting on new coach was drop drastically, Gyokeres become a barren, and not as aggressive as when trained by amorim.
So for this season, Amorim has a target to build a team first, Then after the team is solidly formed, he will start with confidence in the next season.
I agree with you, because a new coach must first build his team before he can achieve success. The players on ground cannot make him achieve his goal and that's why he needs players that will form his team and get the best performance he wants for United. I have also noticed that after Amorim left Sporting, the new coach is unable to put the team on the high level of performance which Amorim left them with.