If realism were as simple as obtaining correct numbers from engineers, we would have hundreds of sims on the PC market. I never doubted that the car doesn't have the correct numbers, those inertia numbers are quite easy to even calculate yourself approximately right from the car model. It is how they are applied in the sim physics engine and how they compare e.g. with lateral grip from tires that makes the difference in feeling. In AC all cars feel heavy, in pMotor sims most cars feels light (except in AMS, which is somewhere in middle). This is because of differences in underlying physics engine, since I believe all those sims use correct inertia numbers for their cars.