Rondo is a fantastic #2 guy on a winning team.
He does everything. He passes, rebounds, defends, scores a little, and isn't afraid of the big moment. All that being said, look at the past six years. The Finals MVP has been a guy who can get his shot whenever he wants to (Pierce, Kobe twice, Dirk, LeBron twice). Rondo is a guy who picks his spots on offense, and prefers to dish than score.
There's nothing wrong with that, but I do think that in order for the Celtics to win, Rondo is going to need to be paired with a scoring whatever (big, wing, maybe even another guard). That guy is going to be the #1 guy for the Celtics if they want to win.