I get what you are trying to say here, but I disagree with it.
1) The gulf between Perk's offensive limitations and Rondo's is vast. Rondo is inconsistent with him jumpshot and is not aggressive enough at the end of the game because he is so bad from the line. But Perkins can't shoot outside 10 feet, can't shoot inside 10 feet either, has some ugly moves on the block and struggles to go up with passes underneath or with offensive boards. So while Rondo may have offensive limitations, Perk is a liability.
2)Rondo controls the touches and egos of 4 HoFers, he is in charge of the Celtics offense, gets the guys the ball where they like it and is responsible for the tempo the C's play at. It takes much more time to build that type of chemistry than it does to plug in a second string forward and center. New PG and everything changes.
3) Say what you will about Rondo's eagerness to make steals and how that results in sometimes poor on ball defense. It's a fair point, but he plays passing lanes well, is fantastic on the double team, and fights through screens. DWill may give you similar effort, but Nash isn't fighting through screens or staying in front of anyone.
4) Monta Ellis is a terrible player with great stats. He is inefficient as they come and has no interest in playing defense or sharing the ball. If the C's traded Rondo to bring in Monta, I'd consider turning in my fan card.
5) A lot is being said about Perk's toughness, aggression and defense. IMO this is becoming a classic case of confusing correlation with causality. Perkins embodied the toughness and grit of this team but he was not the reason for it. This team isn't going to lose it's defensive identity now that he is gone.