Never said they didn't contribute, they were limited players. Do you disagree with that?
Depends on your definition of limited. I still think it is unacceptable that a player like Fellaini that has a decade of PL experience, in the top 6 club like Everton, and playing for one of the biggest clubs in world football will be known for cheating the ball which isn't a skill given his height advantage.
Park gave us more than that and despite the other superstars we had, you could feel his absence. He wasn't a physical specimen b but he gave us what Kante gives Chelsea to an extent. He got involved in some free flowing football. He is a level above Fellaini technically and tactically. Every team would love a Park rather than a Fellaini.
Brown was not spectacular but he made major contributions to our side especially that season where he was probably our most important defender at RB, which isn't his primary position. He was on top form for a whole season, not a few games. And when you consider the calibre of Vidic and Rio, he filled in when required.
O'Shea may have been the weakest of the three but there are only a handful of times in his long career with us that I saw him in the line up and freaked out. Yes, he was a jack of all trades and a master of none, he played many positions well to an acceptable standard. With our Fellaini, he doesn't even know his best position. He keeps saying he's a #6, Moyes thinks a #9.5, LvG #10, Wilmots and José thinks an #8, sadly all of them failed miserably in recent years trusting. Thankfully, José will be smarter.
Every player will have their uses and perform from time to time, even Obertan but at some point it will be required to do more than the basics.