Yeah, it's a tough call. Hazard, Lampard, and Ramires are the only 3 midfield players who have played all 270 minutes in the league this season. Oscar pretty much too, except he was subbed off one game.
Lampard is old and likely won't see action in every game, so then there's Ramires and Oscar. Oscar should have been a shoe-in, but if his starting position changes and he doesn't play where he played last season, he might not play as often.. or he might? I hope he does, but there is just so little space for our players..
It looks like Ramires might be a decent bet then in terms of league minutes played, but he doesn't exactly get that many points either. So you're back to Oscar then
If Hazard's injury isn't so bad, I would go with him, with Oscar as a backup depending on how he finally settles into the squad and where Mourinho sees him playing over the long term. You're right that if he ends up playing deeper that he won't get as many points though = The position Ramires is in in terms of fantasy points.
David Luiz should also be another good Chelsea player to have, once he gets back into the groove - I expect him to play every game once fit. Then again Mourinho might have other ideas. That guy can be unpredictable