Gerrard and Lampard score twenty goals a season and are usually top of the charts when it comes to creating goals for there teams. Cahill's an important player, he's been excellent for us, but he's nowhere near as important to us as the likes of Lampard and Gerrard are to there teams.
He's an excellent player when he's got creative midfielders behind him, as he proved throughout his Everton career. When he's expected to do it for himself and provide for others he simply can't do it, as this poor run of form has shown.
Arteta and Pienaar are more important to us now, when these players are playing you want Cahill playing, because he's clearly an excellent weapon to have. I'd have him over Fellaini, at the moment.