LuisNaniencia
Sky Sports called my bluff
FFS, swore I wasn't going to post in this thread. But come on now, Fellaini can't do what Matić did for Chelsea under Mourinho (for the most part until the collective meltdown last season). The latter operated as the foil for the defense, has great positional sense, seems like someone with natural defensive nous, reads the game well, and was the glue that held the team together while Cesc roved forward when they won the title.
At one point he was the leading tackler + interceptor in the league (ahead of Schneiderlin at Southampton):
He was key to their passing from deep - frequently instigating counter-attack, recycled the ball well, was incredibly mobile for a man of his stature evidenced by his dribbling into space in effortless fashion (completed 43 of 53 dribbles), and extinguished dangerous opposition moves.
Marouane is ill-suited for the deepest midfield role - one that places a great burden on him, in terms of positioning, clean tackling ability, and 'vacuuming' the clutter. Weird comparison - but Matić is a bit like Thiago Motta at his peak for PSG - someone who keeps the engine purring smoothly, and does most of the dirty work silently.
That's far removed from Fellaini's best role - he is more of someone who does his best work in the transition to the final third, or further up. It's not a coincidence that his best season at Everton came as a #10 of sorts, and that has also been his best role at United - as the left sided box-to-box to switched to a #10, not as a holding midfielder like Matić. Above all else, he doesn't have the discipline or defensive intuition to do justice to that pivotal role.
Just for the record I was only asking the question, not stating my belief. Very comprehensive answer.