I want to challenge the premise of this thread.
I think considering the role that Green has been asked to play (or perhaps the lackthereof), Green has done fine.
And often I get the sense that people judge Green's performance entirely on whether he reaches 14, 15, 16 or more points. That's silly, if you ask me, because Green's deal has always been that he's pretty good at a lot of things but not elite at anything in particular. He's not going to be a prolific scorer unless he has a good matchup in a particular game or a particular stretch of minutes. That's just who he is, and we have to learn to accept that. Green is NOT Paul Pierce -- i.e. a natural born scorer -- and we should not expect him to suddenly become one.
Green can score 7-8 points and still have a good game if he plays solid defense, maybe gets a block or a steal, makes some hustle plays, and generally helps keep the team stable for 18-20 minutes while Pierce is not playing.
Green can be living up to REASONABLE expectations even if he's only averaging 10-12 points per game in 20-25 minutes.
Despite all of the gnashing of teeth about Green's contract, the bottom line is that he's a better SF backup than the vast majority of teams in the league have at their disposal. Show me a list of all of these great role players who are better than Jeff Green playing for the minimum or bi-annual. Most of the highly productive, athletic players on cheap contracts are rookies.
Green's ability to give quality minutes is important for this team moving forward considering that Pierce is too old to spend all of his minutes defending LeBron or Melo and still have energy to carry a large load on offense. That's why Danny traded for Green in the first place.