Last night, Rondo was solid as a passer, mediocre defensively and terrible shooting the ball. Rose's block party had something to do with the last bit, but some of it was just Rondo being off.
Anyways, I agree with the OP, although I'd say that Rondo is co-MVP with Garnett. Pierce and Ray are very capable of scoring, but they generate most of their opportunities for themselves. When Rondo and KG are aggressive and effective, they can lead a team attack with their playmaking and spillover defensive energy. Pierce can do some of that, too, but not as frequently.