Ratings are a 10,000 foot view. When your players get better, so do the ratings. But the game is about individual matchups for the most part. USA Offsite had some really good analysis back in the day that is engrained into my memory about formations and percentage of matchups.
80% was PG-PG, SG-SG, etc. but zone defenses are different and sometimes your C gets isolated on an outside player even with man to man. You can see in-game what is happening because it will say "Player X takes a shot closely guarded by Player Y" which means they are comparing shooting of one to defense of another.
Assisted shots are the best in the game because they are "unguarded" so will work more like free throws. There is an unconfirmed theory that assisted shots are actually compared against the ratings but I have my doubts.
All that said, outside defense is THE MOST IMPORTANT stat in the game. Because it stops not only outside shots, but also works against flow to create turnovers and prevent assisted shots. You cannot win consistently without sufficient OD in my opinion.