I think it would be worth knowing more about the characteristic of the 'on' vs 'off' games before I drew any conclusions here.
For instance, in good vs bad games, which position was he playing mostly in? SF or PF? Who else was on the floor with him? Who was the PG? Was Pierce also on the floor?
If you look through the various 5-man lineups that Green has played in, there is a huge variance in performance and not all those differences are due to Green:
http://www.82games.com/1213/12BOS8.HTM#5manLook closely at that list. Right off the bat, his highest-minute lineup (with Barbosa, Lee, Sully & KG) is flat. A Net Rating of 0. The definition of overall mediocrity. .500 ball. Some good play. Some bad.
But if you swap out just Barbosa and replace him with Rondo or Terry, then suddenly it becomes one of two lineups that have been awesome: Net Ratings of +56 and +38, respectively!!!!! (Points per 100 possessions)
Obviously those are not large sample size, but they are big enough to illustrate the point that there are big ramifications to small changes in the lineup. And combined, the two mentioned lineups with Rondo or Terry at PG total to 73 minutes. Still not huge, but a decent sample (a few hundred combined offensive and defensive possessions).
I would bet that when Leandro is running the offense at PG, his tendency is to just drive the hoop. Maybe the occasional pass, but he is first and foremost a scorer and not an offensive coordinator. Terry and Rondo are more likely to try to actually run plays that use their teammates.
Basically, I think that as Doc can finally settle in on which lineups work best and when to use them, the efficiency and consistency of all the players, not just Green, will improve.
And finally, we should not forget that exactly one year ago today, Jeff was lying in a hospital bed with tubes and monitors attached, a bandage covering the big line of stitches in his chest.