I hate those 'a PG has duties' arguments. That proves nothing, it doesn't say in the rulebook that a PG needs to do so and so, there are different types of point guards and the most versatile point guards are generally the best ones in the league. People get caught up in the assist numbers with Rondo and I get it, he's a terrific facilitator but I will never understand why people place him above CP3 in the point guard rankings.
Like Deuce King mentioned above, Rondo is the product of a system (to Rondo's credit, he's great at running it and he is able to make plays on the fly as well). But the Celtics' offense is so solid because of their positioning on the floor; their players pick their spots perfectly and that enables Rondo to penetrate easily through the lane to find teammates, that's why they get a lot of open looks on the floor. Some of the credit should be given to Doc Rivers for establishing a successful offensive system like that.
On the other end, we saw how predictable and disorganized the Clippers' offense was when the Clippers were on that losing skid in - I want to say - March as they kept abusing the PnR and opposing defenses eventually adapted and were able to stop them. CP3 finally detached the shackles and started running the offense on his own terms and the Clippers went into the playoffs looking very strong. Still despite everything last year, CP3 was the most efficient point guard (and in fact the most efficient player in the league not named LeBron). Not to mention he's arguably the most clutch player in the league (I believe he's putting up 42 points per 48 mins of clutch time). Add to that, his ability to shoot, score, pass, even rebound at his height, poke loose balls, etc. I don't know how ANYBODY can say Rondo is better than CP3.
I do think however Rondo was the second best point guard, and that's not to take anything away from Deron Williams who is my favorite out of the bunch. Rondo really turned it up last year and had some terrific performances and I gotta take into account, even with the talent that Boston has, they went through a lot of injuries and Rondo was still able to help lead that squad with Garnett to a win away from the Finals. However, 10 times out of 10, I'm picking Deron over Rondo on my team, he's simply better in a lot more facets of the game. Rondo's inability to consistently shoot from mid-to-long range hurts him.