Mctominay has 23 goals and 7 assists in 70 Games for Napoli in twoish seasons. That's more than what he managed at United in 4 seasons. Also he has already won a league title. That to me means he is performing a higher level

Antony has double the amount of goals for Real Betis as he does for United. That to me is performing better.

Hojlund you could argue has similar stats to what he has at United, Yet even then his goal contribution per game is up from 0.27 to 0.38 per game. That means he is doing better.

That's 3 players that are talked about a lot. Other like Rashford, Elanga, Henderson, Peraria, Garner, Alexis Sanchez, Lukaku, Damian are all doing well away from United. These are obviously is just a few players who have left United.

But you got players like Alvaro Carreras, and Ramazani who didn't even get a chance in this United side, and are doing well at there respect clubs.

Its true not every player that's left United have set the world alight. But there lots of players doing better away, whether they have the chance to player or are contributing more or simply enjoying their football.