No. Jeff Green hasn't "arrived".
He's been pretty consistently solid since his 2nd season in the league. His per minute numbers are on a par with anything he's ever done.
Per 36 minutes; 16 points, 5 rebounds, 1.2 blocks... career averages of 15 points, 6 rebounds, .7 blocks ... so he's actually scoring better in Boston than he's ever done. There's only so much he can do averaging 23 minutes a night, though.
In Seattle, I noticed that in the rare games when Durant sat out, Green consistently put up 20+ points.
In Boston in 4 games that he's started he's averaged 35 minutes, 24.5 points, 5.5 rebounds, 2.8 assists, 2.3 blocks, 1.3 steals 62% shooting, 62% from three and 79% from the line
That said, don't expect him to put up 20+ a night coming off the bench for Paul Pierce. He'll never "arrive" until he's consistently starting and is the 2nd or 3rd scoring option on the team. At that point, he'll be averaging 19 or so points and will be a fringe allstar... a Danny Granger type. He'll probably never actually make an allstar team, though. He's been capable of that for a few years now and he'll continue to be capable of that for the next 5-6.