Just like you said number 7 is a iconic number for Manchester United because those who are given that number the fans will considers they are special player and probably the reason why Manchester United give number 7 to Mason Mount because they want Mount could be a key player for this team and help Manchester United to gets the trophies but the previous players who use this number mostly could not play up to expectations and the players such as Edinson Cavani, Alexis Sanchez or Memphis Depay that they have failed to show their best performance when used this number but i won't judge it early because new season still not starting yet and after the league begin then we will see whether Mason deserved to use that numer or not
Since the era of George Best to Cristiano Ronaldo, the number 7 at Man United was considered a privilege or iconic number, most of those who wore it were important superstars even though some also appeared less than optimal. Former Man United players who have successfully worn number 7 and won many titles are George Best, Bryan Robson, Eric Cantona, David Beckham and Cristiano Ronaldo.
After the Cristiano Ronaldo era at Man United there were several last names who wore number 7 but had difficulty shining. Michael Owen, Angel Di Maria, Memphis Depay and Edinson Cavani lack shine and often appear mediocre. Before moving to Man United, Mason Mount wore number 19 at Chelsea, can he be the perfect successor for Ronaldo or vice versa?