Everyone has already seen that United is a swamp, so it will be extremely difficult to lure any promising player there (not to mention top players).
This is an extreme exagerration. Joining Manchester United is still far better tha joining 95% of the rest of the club around the world and thats a fact. Although Manchester United is currently not in any way potentially to win any of the top trophy, its still a pretty good club. The only reason why it seems like we are pretty bad right now is because Manchester City with Pep is over dominating the league and not to mention that currently Liverpool is pretty good as well
95%? Well no, there are dozens of clubs that are better than Manchester United, more promising. I doubt every player who wants to develop will choose MU as their future club, that wouldn't even qualify for euro cups. The other thing is if they change coaches and prove they haven't stopped being a top team