All those names you list are squad players sure they had runs in the team but they never really elevated themselves to players who were guaranteed to start and I would put Fellaini in that category.
I agree you dont need world class players in every position but look around at the top sides in Europe and they are stacked full of quality in midfield, that is the one area of the pitch where an emphasis is placed on top quality in every position and why they are able dominate possession and win more often that not against English sides, we aren't near that level yet so Fellaini has his place but if we start to improve it's almost guaranteed he will be phased out of the starting line up.
LVG will have learnt two things from fellaini this season, firstly he can use him in the squad and secondly if Strootman gets himself fit he is more of a priority signing than ever because someone who can add physicality and pass the ball a lot better will be a huge asset in the premier league.
I don't think that is a criticism of Fellaini, like a number of others he will play his part but realistically in the summer two or three players are going to be brought in to improve the first eleven to try and take the team to the next level he won't be alone in being more of a squad player going forward.