Playing with McTominay in midfield is essentially like playing with 10 men. He provides nothing in a midfield role, he passes and hides, the 25 or so odd passes he might make in a game. He doesn't have a range of passing; it's short sideways passes and nothing else. He has no defensive abilities as a traditional #6, he doesn't have good positional sense, to cut out a pass, he can't take the ball of the defenders and advance it up the pitch, he is big and imposing, but his only real defensive ability is his aerial strength, which is only really useful in defending set pieces. As far as an attacking midfielder he doesn't have the technically ability to make a line breaking pass or intricate through ball, he can't dribble past a player, he doesn't create chances for others. So basically, the only thing he can do is burst into the box and score the odd goal. And while he did that last year, I don't know how many chances he actually took off of our attacking players by getting in their way and occupying their space. He likely prevented as many goals from other players as he did score for himself, to me he is a net negative, or net neutral to the team, at best, in that role.
Seems like a great guy, coaches love him, players love him, he had a great attitude, he loved the club, he never complained, but he just plain and simple wasn't good enough. Replacing likes of McTominay was one of the major factors in trying to upgrade this team, now we didn't, but that's not due to McTominay leaving, it's due to the ineptitude of replacing him with the right players. But if we wanted to advance as a club moving on an extremely limited player that only ever got the chance to play for United because he came through the academy was key to that. Think about it this way, if McTominay had never played for United, and was currently having the season he is having for Napoli, would there be a single United fan in the world that would be identifying him as the key player we should be signing this summer?