He might be, but it's going to either be totally subjective, or I think you have to acknowledge that on the primary measure - assists - there are a few guys who might be able to match him. I think the clear competition is Paul. He gets at least 90% of the assists that Rondo does, while being a far superior scorer. Whether you think his scoring gets him "easy" assists or not, is there any doubt that if he focused on them as much as Rondo he could get 1 or 2 more per night? With the exception of this year, Nash has produced more assists per minute by a comfortable margin as well. I do think he edges guys like Williams, Calderon, Rubio by a small margin.
What's special about Rondo, to me, is that he is an elite talent in EVERY category except for as a scorer. He's an elite passer AND rebounder AND defender. That's why he can go nuts in the playoffs - I don't know if there is a single player in the league who can dominate in more than 3 major categories at the same time, and I can't think of another PG with that ability. He won't do it every night, but he's capable and that's worth something. Paul won't go out and grab 15 rebounds or check the opposing team's best scorer. Rose won't dominate with the pass or play lockdown defense. And so on. Doesn't matter if Rondo is the best passer in the game, but the fact that he's at or near the top in 3 major categories when he really needs to be, is special.