Both are the playing the same position. One seems to be under achieving and is paid a lot but is a proven talented, borderline all star while the other has shown he's really good but can't bring it consistently. Both can play very good defense, Gay seems to be better at creating his own offense but Green seems to be more efficient. Both are athletic.
This does not describe either player.
In a league where featured 3s are rare, Rudy Gay is absolutely a borderline all-star, or at least has played so in the past . Questionable effort, poor shot selection hold him back, but keep in mind Paul George wasn't any better offensively last year.
You can count the number of featured SFs in the league on one hand.
Lebron
Melo
Pierce
Durant (not in this order of course)
Iggy
George
(Cue Princess Bride references)
Then who? Deng, Batum, Leonard...they're all at best the third best players on their teams. Rudy Gay and Jeff Green both will likely be the best or second best player on the floor for their teams during large chunks next season. After them it's all specialists or clear second tier players. Gallinari, Parsons, Barnes, Harris..those guys could 'make the jump' next year, but haven't yet and all of them outside of Harris will play a clear third or fourth fiddle coming into the all star weekend.
George was much better offensively. His true shooting percentage and eFG were 53.1 and 49.1; Gay's were 49.4 and 44.9. George's percentages were slightly below-average while Gay's were well below average. Then George averaged 4.1 assists to Gay's 2.7.
The number of featured small forwards means nothing. Gay has rarely played to the standard of an all-star.
George's %s are better solely because of his slightly better 3pt%, and Gay's poor shot selection in a bad year.
You got me on assists though.
But my point about featured 3s is relevant to the all star arguement. Look at Jrue Holiday, or Caron Butler, or dozens of other dubious all-star selections. If you're the featured guy on a bad team at a shallow position you got a shot.
Why does it matter why George was more efficient? I guess it could if it was based on fluky shooting but George has been a good three point shooter two of his three seasons. I think it's reasonable to label him an above-average three-point shooter. Gay was a solid shooter from deep early on in his career but has dropped off, which may be related to his shoulder or vision problems. I wouldn't project him to shoot better from deep than George next season. As such, I would expect George to remain a more efficient scorer. If George can get to the line more like he did in the playoffs, he has the ingredients to be a very efficient scorer. Regardless, factoring in their efficiency and assists, George was significantly better offensively than Gay last season.
Also, your comment about Gay having poor shot selection in a bad year makes it seem like it was an out of the norm season. He's always had bad selection. Even when he shot in the mid-forties, he always settled for deep-deep 2-pointers. Last season was regular Rudy Gay with worse shooting.