If you look carefully, outside of the Heat, the second option is typically not very different from the third option, and when it is, the third option is much further from 17 ppg than the second. Also, Lamar Odom player 37+ minutes in both years when he averaged 17 ppg. Not to mention that he was 5+ years removed, 30+ years old when he played on those LAL championship teams, so I don't see this as being too relevant to the discussion.
I'm curious how you have decided that Green will average 17 pp36 as the first option. He posted ~18.4 pp36 as a second gun to Paul Pierce (20.2 pp36) over the last three months of the season. If he sustains this, it is better or at least as good as most second guns on recent championship teams (Wade excluded).
Again, he won't be a transcendent number one scorer, but calling him "average" and "fifth player on a good team" is a mischaracterization of what he is.
Actually most title teams have a 1 and 2 and then there is a pretty big drop to the 3. Dallas was an exception and the most recent Lakers teams were to an extent, than Pau was basically the same level scorer as a #1 in Memphis as he was as the #2 in LA. But historically you have Wade/Shaq, Shaq/Kobe, MJ/Pip, even the Spurs Parker was closer to Duncan than he was to Manu in the last title team (and Robinson and Duncan were clear 1/2 for their first title), and even Rip & Billups were closer than Sheed was to Billups during the season.
Title teams are generally 1/2 with a solid 3rd contributor. When you start looking around the league at who that 3rd contributor has been, Jeff Green doesn't measure up. He isn't Bosh, he isn't Allen, he isn't even Odom or Bynum, he isn't Ginobli, he isn't Chandler, he isn't even Sheed. He might be a Toine in Miami or a Rick Fox in LA, but both of those guys have had far better peaks than Jeff Green.
Jeff Green was basically the 2nd option in Oklahoma City (for the first two seasons and the third option his last two seasons) playing 37 minutes a game and couldn't even crack 17 ppg. Now granted he was younger then, but he was also playing with a dominate scorer in Durant that could take some pressure off of him. He was a 17 point scorer in 34 minutes the last two months, but he was also well above his career best from both down town and inside. I would expect his shooting to normalize back more towards his career averages (especially with an increased focus on him), which would put him right around 17 a game with an extra minute or two.