I disagree.
In a 1-3-1 zone, the PG is weighted heavily for OD. The SG, SF and PF are weighted medium for OD. The C is weighted light for OD.
If you play your center to defend as a PG then he will take that top spot and will be weighted heavily for OD.
I agree that the player that is covered in a zone is slightly randomized.
You are talking about the calculation of team ratings, not how the game engine simulates individual possessions.