He isn't really though. He's a lot shitter than them, inherently. Occasionally he can play better than them, but at his very core, his very essence of being is of one significantly shitter.
People don't like him because he represents not just shitness, but a particular type of plodding, lumpen shitness that should never have been anywhere near a club like Man Utd. Schneiderlin, Memphis and Darmian are merely not good enough versions of the kind of players we want. Fellaini is a not good enough version of the kind of player we don't. It may be a little unfair to boo him, but it's disingenuous to pretend he doesn't occupy a very singlur status amongst United fans. He's a totem for shitness. The bad kind of shitness.