We Only have three "Real" NBA Players on this team.

[Vermont Green]

I think Green does have mitigating factors which could allow for an advancement in his production.  His time in OKC, he was playing out of position.  His arrival in Boston was mid season and he never really fit in.  Then miss a whole season due to open heart surgery and yeah, you can expect the first half of the season to be less productive than the second half.

I don't know how much more ceiling he has though.  What I see on the court is potential still but I am not sure if he is going to realize it no matter what his USG% is.  It just seems that there is always something that finds a way of preventing him from getting better (heart surgery is of course in a category all its own).  I don't know if he has that extra something that is needed to just play through the mitigating factors and get better anyway.

He is a real NBA player though, I don't see how that could be in dispute, and one that may get even better.

[BballTim]

I'd be really interested to see some examples of players who were thoroughly average and not especially efficient through their first 5-6 years in the league who suddenly turned into really valuable contributors.

Chauncey Billups also fits this model, since he didn't really explode until that playoff series with the Timberwolves--right before he ended up in Detroit.
http://www.basketball-reference.com/players/b/billuch01.html

Steve Nash also fits the going definition of "average" pretty well up until he moved to Phoenix.

Nash just started shooting more about his 5th year in the league, but was basically the same player (just more shots) his entire career.  Phoenix ran such a high tempo that Nash's totals increased, but he was nearly as efficient in Dallas.

Billups basically just improved his shooting percentages (and was continually doing that) a couple of points and that is all it took for him to up his scoring.  He was basically the same player on a per minute basis his entire career (with modest shooting increases) who finally reached his peak shooting in Detroit and who happened to be surrounded by a bunch of other quality players (a big boost for a PG).

I just don't see Green all of a sudden becoming a better shooter (when history doesn't show it).  He has had the same role with the same minutes virtually his entire career and hasn't improved much in those areas.  It just isn't going to happen all of a sudden.

  If you're claiming that Nash and Billups were the same players when they were 25 than they were years later when they were all-nba players (or MVP) then I'd say that your post is an example of being able to get stats to say whatever you want, no matter how far-fetched. As for Green, are you really claiming that his role on a Celts team without any good scorers around him is the same as it was when he was on the court with players like Durant and Westbrook? I don't see that as very likely at all.

[Celtics18]

16, 6, and 2 with a field goal percentage above .450, and a block and a steal a game.  I'll take that out of Jeff Green. 

More would be a bonus, less a disappointment.  As far as being a "real" NBA player;  No question, Jeff Green is a "real" NBA player.