I agree that during our championship run in 2008, the 20 year old, second year, Rajon Rondo was a role player, a very good role player, but a role player nonetheless.
During our Finals run in 2010, however, Rondo was arguably our most valuable player. He was almost indisputably one of our top three. Again in 2012, he was arguably our best player, almost indisputably top two.
In 2009, he was the best ( I guess you could argue second best) on the team that was a game away from reaching the conference finals.
In 2011, he played like a star in our first round series against the Knicks, probably our best player. He started slowly in the Miami series, and then of course suffered the infamous take down by Dwayne Wade, which effectively ended any chance we had to advance beyond that series.