The problem with these comparisons between Rondo and Westbrook, D-Will, etc. is that they get paid much more than he does. Do we want one of the two star players on a max contract, that we can afford, to be our pg, or should it rather be a wing and a big?
It's very rare that point guards win championships, because their main role is to distribute the ball and get the team the most efficient option on offense. If they are first option as scorers as well, they have to be in the Derrick Rose category to be really effective.
Westbrook thrives because he is the 2nd option. I'm not sure that he knows that.
Rondo would be looking really good if Pierce, KG and Allen were scoring 19, 17 and 16 points per game (less than their championship season). But they are down to 17, 14 and 14. Rondo is scoring 15 points per game, making him one of the main options on offense.
That never used to be his role, so he is still learning to balance things out (and half the time being told to score more and half the time being told to get everybody involved).
Westbrook would have the same problems as Rondo in Boston, except that he would be the first option on offense. Would he more efficient than Rondo? I really doubt it.
We joke about bad contracts (Rashard Lewis, Joe Johnson, Gilbert Arenas before he got amnestied etc.), but the reality is that our own big 3 are now overpaid to a degree that we can't get the pieces to make this team a contender this year (unless someone throws us a freebie). Rajon Rondo on the other hand has a contract that allows us to pay two top star caliber players to lead this team, with Rondo as the all star point guard who can get the job done better than most others in the league.
So I wouldn't trade Rondo for Westbrook.