I agree completely with you on most of this.
He needs to become more consistent but I sat down earlier today and this bugged me why he's like this...
Is it maybe because he's playing with 4 Hall of Famers that he feels he doesn't need to contribute as much as he could? I doubt it's laziness, maybe more fatigue in recent games.
For instance if he was playing for say the Clippers or Raptors do you think he would have a greater influence on games due to the lack of household names?
Its impossible to know, so its all speculation.
I personally think part of it is self preservation. He has been playing with veterans who understand how to keep themselves fresh and healthy, and I think at least part of it has rubbed off. He knows that if he is going to play so many minutes, he can't go all out (and play wrecklessly) all the time, so he picks his spots. And granted, he generally picks them pretty well.
Although, I also think at least a small part of it is ego. I think he genuinely gets revved up to "prove" himself against other elite players and teams. But, against teams and players where he does not feel he has anything to prove it against, he doesn't seem to have that drive to kill them.
The interesting thing is that its kind of the opposite of what we see with KG. He absolutely loves to destroy guys who he doesn't think deserve to be on the same court with him. While he doesn't back down in big games, he just gets that special gleam in his eyes to destroy guys who aren't as good. If some of that could rub off on Rondo, I think he would become a much more complete player.