On the topic of "some additional factors", here are some of the notes that accompany the formulas on the basketball reference site:
"The core of the Defensive Rating calculation is the concept of the individual Defensive Stop. Stops take into account the instances of a player ending an opposing possession that are tracked in the boxscore (blocks, steals, and defensive rebounds)."
"Out of necessity (owing to a lack of defensive data in the basic boxscore), individual Defensive Ratings are heavily influenced by the team's defensive efficiency. They assume that all teammates are equally good (per minute) at forcing non-steal turnovers and non-block misses, as well as assuming that all teammates face the same number of total possessions per minute."
Until we have player tracking in college basketball, it's difficult to do much better than something along these lines for defensive rating. So take these with a huge grain of salt.
As for offensive rating, it should be taken in context with player usage (and, in my opinion, a player's teammates' offensive rebounding % would ideally be removed from the formula)
