I think its a lot simpler than people are making it. Rondo has flat out struggled in 3 areas from what I've seen. None of them even start with oustide shooting.
1) Aggresiveness - He's just passive out there. Not sure if its injury, or what it is. When he's not his aggressive self, the offense falters, his assists go down, and his scoring is non existent. He was more aggressive at times the last game out.
2) Shot clock - Tommy pointed this out the other night, and its been consistent throughout the last 10 or so games. Rondo is holding the ball way too long, almost down to the 10-14 minute mark on the clock without anything happening. Not good. Can't keep starting your offense at the 12 min mark.
3) Dribble penetration - He points this out in the article above. He lets his man get into the lane time and time again, putting a ton of pressure on KG, Krstic, or BBD to cover it, or get a foul because of it. This puts are bigs in a terrible defensive spot game in and game out. Not only are they covering their man, or trying to, they have to stop ball because of his defense.