Been looking at some stuff on the DVR, and I'll throw this out as a theory:
I wonder if Rondo clearly understands his role on this club sans Garnett. With three premier scorers on the floor, his role is admittedly more deferential than it is now, when essentially he fills one of the three scoring roles. It's easier to survive offensively with him taking a passive distribution role with Garnett on the floor.
With just Pierce and Allen, though - two players who rely a bunch on where they get the basketball on the floor - the role changes to more of a creator, and I'm not sure he grasps that. With Davis instead of Garnett on the floor, the offense comes to a screeching halt when Rajon pounds the basketball at the top of the key. It works pretty well, though, when he's probing off the dribble, testing his man and reading the screens and curls.
His game isn't mature, as I see it, primarily in situational recognition and response. I categorize response to adversity in that vein, also - he hasn't been the same since the Brad Miller foul. I wonder if you just don't sit him down, tell him forget it and simplify direction: We need you working the basketball off the dribble and defending like a madman. If you're going to make a mistake, make it at full speed. I really don't think you need to tell a pro that, but Rondo's running the offense like Garnett's on the floor and that is no longer a winning formula for us.
Just play, man.
I'm not ready to buy into any great, deep conspiracy on Rondo's decline. I think we have to at least entertain the notion that he's confused.