Perhaps the PI system is not quite as 'broken' as many claim ( missiles aside ). There seems to be mounting evidence, like Spiny's D class Civic, that cars at the same PI are competitive with each other, not at the track level but, at a global level only.
In other words, while one car may be a 'leaderboard car' at certain types of tracks, they maybe weak at others. So, if you run every race in the game with that one car, it may run a nearly identical cumulative time to another car of the same PI that has different strengths and weaknesses.
Perhaps that was T10's goal, and the cries of "The PI system sucks because my A850 car isn't competitive with your A850 car at track X" are based on a foolish assumption....