Even if I will agree with you that Manchester United can be regarded as graveyard of players, it is so cool to understand that there are some strong and exceptional players who can still fit into the current situation of Manchester United. Player like Bruno Fernandes has been flourishing despite the continued poor performance of Manchester United.
This could also mean that Manchester United doesn't need upcoming players like Garnacho. They need proven players like;
Osimhen,
Salah,
Vini Junior,
Mbappé,
Lewandowski,
These players cannot flop in any club.
As a club, you cannot solely depend on these kind of signings, there are financial policies and rules in place that control transfer spendings so most times you also have to sign upcoming players. I think one problem with Manchester United is that they lack the ability to identify players they need and that can fit their playing style and strength.