I think average is harsh JBG. But he's not in Sami's class.
For me you have different moulds of players.
Obviously some are better than others but they are all similar in there strengths and weaknesses. IE.
Midfield playmakers:
Scholes, Murphy, Jenas, Lampard. Lads who can score goals and see clever passes, they can defend and do defend but aren't great at it. On a lesser level the likes of Koumas and Bullard.
Box to box ball winners:
Keane (at his best), Gerrard, Essien, Davids and Gilberto. Again lesser players in the same mould, Parker and Smertin. Players that love a tackle, cover every blade of grass and try and make things happen.
Holding midfielders and holding midfield playmakers:
Vieira, Alonso, Hamann, Makelele. On a lesser note, Carrick, Butt etc. Holding midfielders meaning players who simply break up attacks and the playmaker bit meaning they set up attacks from deep positions like Guardiola and Alonso with intelligent passing and vision aswell as breaking up attacks.
Commanding centre halfs:
Hyypia, Ferdinand, Campbell, Terry. On a lesser note players like De Zeeuw, Ehiogu and Upson. Players that are good in the air and hold there position well and marshall a defence. Usually captain material and good leaders.
Sweepers:
Carragher, Henchoz (at his best) Gallas, Boumsong, Toure, Carvalho. Players who make last ditch tackles, sweep up and cover the main figure of the defence.
For me, to have a winning formula for a team, you need alot of qualities and you need to take into account all types of player, all qualities of players and the formation you want to use. If you're adopting two centre halfs then realistically you MUST have one of each otherwise you'll lack in one department.