Let’s for a moment assume that you are correct. Then two cars with the same PP should be equal in performance, right?
Here is an easy experiment I did, you can do the same if you want to verify the results independently. I bought two Toyota 86 GT and tuned them both to 550 pp.
With the first car I achieved this by making the car as lightweight as possible, maximising downforce and fitting the grippiest tyres, best brakes, and sports suspension, then adjusting the power limiters until I reached the desired PP limit.
The second car was tuned by maximising the power output, fitting sports soft tyres and then adjusting to 550 PP by adding ballast.
We now have one lightweight, low power, high grip car, and one heavy, high power and low grip car. Both have the same PP. In this scenario, which do you believe give you better information about the performance of these two cars: The PP score or the acceleration and cornering data?
Next, I took the two cars to High Speed Ring and did three laps in each of them. To my surprise (not really) there was an 8 second gap between the two cars. How is this possible when they have the same PP score?