As I mentioned, what happens after the ball's initial landing is determined by the contours they have recorded for the portion of the course in play (including the greens).
As for variability, that is accomplished by introducing random variations. This is where the precision, forgiveness, balance, etc., come in. Further, the exact force and direction of the wind can be subjected to a random deviation when the physics calculation if performed.
If the randomness element is normally distributed, the majority of the shots will be somewhere near the "perfect" shot. It is the nature of such distributions that there will be increasingly rare events where the deviation is much greater. These are what I call "WTF" shots. For instance, 68.3% of all results in a normal distribution fall within 1 standard deviation, 99.4% within 2 sd,, and 99.99% within 4 s.d.
The use of VEM deviation, which has been variously admitted and denied, but which is unquestionably the subject of a WGT patent, proposes to vary the performance of an item (such as a club) in a manner coupled with the player's performance level.