Any player is going to be better when playing on a team like this C's team. Being surrounded by great players opens up the floor for everyone else, and spreads the focus of the other teams out.
The problem with Rondo is that he can be gameplanned out of games, regardless of who his teammates are. If teams back way off him, and use his man to play the passing lanes, and not helping off the other perimeter players, it has been proven time and again that it takes Rondo out of what he wants to do, and makes him significantly less effective more times than not.
Of course it does make it slightly harder to do this when all 4 of the other players on the floor can hit open shots, as well as move the ball quickly, but Rondo can still be a liability when teams defend him like this.
So until he becomes more proficient with the jumper, or consistently learns other ways to help his team when this happens (he has been better at points this year, by learning to find weaknesses in the zone, and basically becoming a roamer off the ball), he is not going to be able to take that next step, regardless of his teammates.