This may be very true that the players may not be giving their all to the team. Manchester United will need to sell off some players for them to be able restructure the team and pick young talents who are ready and willing to gibe their all for the growth of the team and their own growth, Amorim is a man who works with building of systems to achieving a long term goal so I believe he is the good person for the job and will need time and resources, two seasons like you mentioned will not be a bad idea at all for him to be able to pull that through.
You have nailed it, United need to lets go of some players, the team is full with outdated players, I think they have to make this decision very faat, it is taking them long time and I don't know what, as it stands the season is starting veey soon, if we look very closely it seems they aren't prepared for next season, eomties I do wonder what's really going on with this club, despite that most of there fans are anti Chelsea, I do like the team, when they were in good form the were one of the teams that made English premiership to be very interesting to watch but in the recent days, it seems the team lack ideas on what to do and am not comfortable with that, I have always said it that amorim is a good coach but I don't think that the management is ready to give him what he needs.