People have already said it but the OP is off because he is trying to argue that people overlook Rondo's weaknesses. Everyone knows Rondo's weaknesses, they are obvious. What the OP doesn't do is look at the totality of Rondo's game. Despite his weaknesses, Rondo is at worst a top 8 PG in the league and at best a top 3 one. The argument that he didn't see a drop off in the PG play with our backups shows that maybe people who are eager to take 80 cents on the dollar for Rondo are not aware of that similarly obvious fact.
Rondo is ideal fit for this team. He's a defensive minded distributor. That's exactly what this team needs most and Rondo is as good at those things as anyone in the league.
Our team does not need a PG who can shoot or a player who can score. Our offense has 3 of the best. What we need is someone to create opportunities for those 3 because they cannot create their own shots like they could in their prime. It would be great if Rondo could shoot and score (and occasionally he does) but that isn't what we need from a PG.
This team might not be the ideal fit for Rondo (he doesn't get to run in the open court as much), but outside of Chris Paul and arguably DWill, there is not a better fit for this team. The idea that we could insert any PG into our offense, and the team would compensate for the absence of Rondo's playmaking ability by having the new guy take jump shots is absurd. That doesn't even take into account that he wreaks havoc on defense.
Our backups have not performed well. They have performed adequately when Rondo has been out. But I'm not sure that any of them have shown enough for me to feel confident of any of them being a back up PG in the playoffs, let alone a starter. And the playoffs are what matters. Championships are what matter. The Celtics have never been easy to defend in the playoffs. Rondo has never been easy to defend in the playoffs.
Did the Lakers exploit him? Absolutely. But that was in the finals against the best team in the league against Kobe Bryant who is one of the smartest players ever. Imagine what he would do to Bradley in that situation. The other team that shut down Rondo was the Heat. They are exceptionally athletic on D and even then, it took Dwayne Wade body slamming Rondo to fully contain him.
Rondo has improved as an off the dribble shooter, but he's never going to be Ray Allen. He's never going to be reliable for 20+ points a game and if he is it means whatever team he's on is in trouble.
It gets stressful, as the his teammates have to expend alot of energy and work extra hard to score points. You could make the case that Rondo's passing gives his teammates easy open looks. But if you think about it, if he gets 15 assists that is only 15 plays he completed. All of his other plays are turnovers, holding the ball, shooting 3 pointers with 2 seconds on the shotclock, etc
Rondo's teammates expend less energy when he is on the court. When Rondo's not getting assists, he's running set plays in the offense, getting rebounds, or giving space for other guys to operate. He makes some bad decisions, and his look worse than most. But blaming Rondo for his turnovers is one thing, blaming him for when other guys don't perform is another. That's what happens way too much on here. When Rondo scores, he should've passed. When he makes a bad pass, he should have made a different pass. When he makes a steal it doesn't count because he plays "lazy" D. When he rebounds it doesn't count because he's playing out of position? (I honestly have no idea why people don't count his rebounding). Somehow Rondo's bad decisions and deficiencies are so obvious to everyone except for the people who have to play with him and against him every night.
The logic that we should trade him for someone who is statistically worse, evaluated worse, and generally considered worse because that player does a few things better than Rondo is flawed. If we can get someone better than Rondo (a top 20 player) for a reasonable price then let's do it. If we can't, let's not force out our best player because of the hope that bringing in someone different will somehow magically make us contenders.