This. He needs two other midfielders around him to make up for his footballing weaknesses and bring the best out of the other two footballers by doing most of the dirty work and providing key support and link-ups between his teammates. That was one of his main strengths last season, at Everton: he provided great support for Baines and Pienaar, allowing both to run into spaces and link up with him whilst he would draw in the opposition with his large frame. Whenever he played in central midfield for Everton, last season, it was as a destroyer and someone who did all of the dirty work. He would defend aggressively and try to win the ball as quick as possible whilst his teammates covered up the spaces he left open.
Here, at Man. Utd., if he is to play in a 2-man midfield, he'll need a midfield partner who has the energy to cover the large spaces Fellaini leaves. Plus, he'll need creative, attacking players around him so that he doesn't have the responsibility to distribute the ball and create chances. In Belgium, he has defensive support from Witsel and attacking support from Hazard, de Bruyne, Chadli, Mertens, Mirallas, etc. In Everton, he had defensive support from everyone in the team (against the big teams), particularly his more defensive, deep-lying partner in Gibson. He had attacking support from Osman, Pienaar, Baines, Coleman, and Mirallas.
He'll only benefit with us if he has 1-2 players fill up the spaces he leaves open when getting aggressive, and he'll be useful on the attack if we have creative attacking players with good movement and creativity.
some people are seriously comparing him to a league 1 or 2 player? I'm a Fellaini fan, and I admit that against the big teams he has struggled but he's not a league 2 footballer. Ludicrous to think so.