Project CARS is in no way a perfect racing game, the simulation aspect of it still needs a lot of work. Weight transfer still leaves a lot to be desired, and is something Assetto Corsa does far better. For example, kerb attacks are very muted in Project CARS, with there being little difference in the suspension behaviour between road cars and race cars.
Crests are also quite poorly done, and you don't get the same "take-off" effect as you do in Assetto Corsa.
However, somebody who doesn't observe these technicalities will see that Project CARS still properly recreates the motorsport environment, which is absent in Assetto Corsa. Setups are much less of a hassle over a racing weekend in Project CARS, and it is generally less frustrating to quickly strategise, like in the final minutes of qualifying.
Overall, both games fall short, not of the simulation experience, but of the game experience. Which is what Gran Turismo will always excel in. I just hope SimBin can observe and not just make a great simulator, but a great game.