I think we kind of have a seperate Offense and Defense rating already..
I think the defense part is about 60-80% of the current rating. High enthousiasm leads to higher defense team ratings (f.e crunch time at 6 or normal at 8). Every time when you see a team play with high enthousiasm the players ratings are high as well and visa versa. A team who plays TIE with 5 enthousiasm will get lower team defense ratings and lower player ratings, while their shooting-% can stay the same.
If you compare players, you may see players with higher shooting-% but still with low ratings because they suck at the defense part. But on the other end you see players with low shooting-% and a high rating, because they defend pretty well.
So a player who made a double-double could still be lucky to pick up 10+ rebounds because his direct defender is even more crap in rebounding. This player still got a 5 rating because he is just a bad defender.
Then the shooting point. The influence of experience is well underrated in my opinion. I bought a player just to make a guess at the influence of experience, now here it is;
Alfreds Jentess
(2650100)Stats;
Jump Shot: atrocious Jump Range: mediocre
Experience: proficient
Shooting-%; 0,571, over 4 games.
A point guard with atrocious JS and mediocre JR who shooting 0,571%. Kinda weird isn't it. I think experienced players have a better look on the shot, they don't take crapshots very often.
A player must decide whether the opportunity presented is good enough to take a shot… this of course changes as a function of amongst other things… the shot clock, the players experience,
You see there are many factors which decide wether your player will shoot or not and wether he will hit or not. I don't think you can say that easily JS + JR + Random Factor = % FG.