Idk man Mata is good but then look at City you've got Aguero, Sterling, Toure and Silva (who in my humble opinion is a level above Mata).
Chelsea only really have Hazard and Fabregas who I would class as game-changing players.
Arsenal have Sanchez, Chamberlain and Ozil.
I know they don't have tons but a few is enough like you said. Right now I ask myself is Rooney really even a game-changer anymore or just a decent player who is a shadow of what he once was? Mata produced some fine moments last season, but lets not forget who set him up for that goal vs Liverpool, Di Maria. Sure you can say it wasn't a great pass on that occasion but having someone who was capable of playing and picking out a pass from anywhere on the pitch was always very useful. Not forgetting the pace he also offered. I'm not saying for any minute we were wrong to sell him I'm just letting you know that replacing him with a player like Pedro is efficient to the team, just like when we replaced Valencia with Ronaldo, but not going to win you matches through creating game-changing moments individually with their brilliance.