Why though?
Other then the whole theoretical idea of "he's not strong enough" what other evidence is there to show that that Bass is a better PF then Green?
Bass shot 230 out of his 632 field goal attempts (36%) inside the paint, and he shot a combined 46% from the field on those attempts.
Green took 416 out of his 817 field goal attempts (51%) inside the paint, and he shot a combined 55% from the field on those attempts.
Not only does Jeff Green take more shots (and a higher percentage of his shots) inside the paint, but he also scores at a much higher percentage from there. This suggests that he is clearly a far more capable scorer in the paint than Bass is.
Green also has a higher Ast% (7.5% vs 5%) and AstRatio (9.5 vs 6.7) then Bass does. So not only is he a better scorer in the paint, but he's also a better passer (and a more willing passer) then Bass. This means that he's less of a liability if he gets outmatched by his defender in the post because he's more likely to find a teammate rather than force up a bad shot.
Green attempts (3.3 vs 2.8 ) and makes (2.6 vs 2.3) more free throws than Bass which means he puts more pressure on the opposing teams interior defense and is more likely to get opposing players into foul trouble.
Bass does have a better rebounding rate (11.6% vs 8.9%) than Green.
You can argue defense, but Green has never had an elite defensive center like Dwight Howard or Kevin Garnett behind him to make up for his defensive mistakes - there's no telling how good he could be defensively in this Boston system.
On top of all this Green's combination of speed + size along with his legit three point range makes him a potential matchup nightmare on any given night.
I don't know what you guys use to determine how good a PF an NBA player is, but aside from rebounding Jeff Green looks like a superior PF than Bass in almost every way.
To rub more salt in the wound not only is Green better at all of those things, but he's also got more potential.
Bass is limited by skill level, but his game is very polished - i.e. he has few talents, but what he's good at he does very well. Because he's already so good at what he does, he doesn't really have much room to improve unless he adds a whole other dimension to his game.
Jeff's game is still pretty green (no pun intended) - there is nothing on a basketball court that he can't do, all he needs to do is polish his game. If he improves his shot selection, decision making and defensive IQ he has all the tools and talent to be a future all-star.
I'm telling you guys now, Jeff Green is a more capable PF then you think...especially in todays league where true post up big men are a rarity.