The software is not always the problem in terms of a correct simulation. It is often a question of lack of data
I was watching a video from Neil's Heusinkveld where he was making the point that its not just the lack of data, but also if we can be sure how accurate that data is.
Aerodynamics is the most difficult to simulate due to its wide range of variables and it is true what you mention when the simplest the car is, the easier it is to simulate it, for example an F1 is more difficult to simulate accurately than a street car. your data easier to get. The Oreca 07 is one of the best simulated cars in rfactor 2 and here is the answer to the data and professional equipment. During various stages we have had feedback from Duqueine Engineering, Dragonspeed and Jacky Chan Racing, and their input was invaluable to making this car.
they got very detailed real data for Tatuus cars and BMW M2 CS racing. You can read about it in official announcements. But perhaps then they also did some fudging for some of the cars to feel right. Porsche did they private 911 GT3 Cup car mod in rF2 for training purposes.