Might not be a lot but ya know, considering he was predominantly a midfielder it's a solid effort.
Kind of. Sort of.
But this is the old "Plan B" discussion all over again.
The fact is that Fellaini was - as you say - predominantly a midfielder for us. He was never used exclusively in the only role he ever truly
excelled in, i.e. as a physically dominant AM/SS of sorts (someone capable of causing havoc in the opposition box as a target).
He mainly played as a midfielder (a CM - even DM at times). And he was utterly mediocre in that role.
Using him regularly, in his best role, would've meant going for a brand of football hardly any United fan would fancy. And keeping him on the books as a pure "Plan B" (a big fecker you send on to cause havoc in the opposition box and/or to defend on set pieces) was never...well, let's just say that his proven effectiveness in those situations was never outstanding enough to make a compelling argument for keeping him.
Bottom line: as a midfielder, Fellaini was never anything but mediocre at best. The most you could say about him in that capacity was that he wasn't significantly worse than the other fairly shite options we had at the time.