judging transfers within just a year is very premature. if you spend 20m+ on a player in their 20s, you're not buying one year of service, you're buying their prime playing years. if you spend that kind of money on a younger player, you're buying potential. either way, at least give them a season to bed-in before writing them off.
any worst transfers list made after just a year should really only be made up of players who have absolutely zero future at the club. Fellaini's been poor, but I'm more keen to trust the very large sample size that says he has talent than the small sample size where literally everything that could go wrong for Utd did go wrong where he played poorly. something like Soldado was far worse, because Spurs bought him relying solely upon his goals to win games and his inability do so completely derailed their season—and even then, I'm not ready to say he's definitively never going to be a productive player in the future.