I am not sure why people think Paul is a worse fit for the C's team than Rondo. I can understand that argument for guys like Rose and Westbrook, but not Paul.
Paul is the most complete PG in the league. He is a great (not good, great) passer, and even if he isn't as good at that as Rondo (which is debatable), he is close. He is a great scorer, and he is a good defender (Rondo is better, but not by that much...they both are kind of trick or treat defenders).
For me, the key with Paul is that he will still be able to get the ball to the Big 3 as well as almost any PG in the league, but he will also be able to make teams pay for cheating off him, which will make things even easier for Ray, Pierce, and KG.
People seem to look at Paul's scoring numbers and think he is a volume scorer. He has been taking on more of a scoring role, because that is what his team needs from them without any other front line scorers on the roster. However, he is always among the top of the league in assists, and is absolutely one of the best "pure" PGs the league has seen, maybe ever.
The one area where Paul is not better than Rondo is defensively. However, this is a bit of a weak case because Rondo is nowhere near as good as he is touted as. Yes, he has the ability to be dominant. But he doesn't dominate defensively with any consistency. He gets beat way too much, and is constantly pacing himself.
Rondo is not Bill Russell, who dominated games with his defense and rebounding for every second he was on the floor. Rondo will dominate for a couple 3 minute stretches, and then be an average defender for the other 34 minutes he plays.
For me, that is nowhere near enough to make up for the dramatic difference Paul would have on the offense of a team made up of aging stars who can't carry the scoring burden nearly as much as they could a few years ago.