So as of now, only 3-5 stats (Acceleration, braking, downforce, handling, fuel economy) make any real difference in the race, and reliability and cooling make literally no difference at all. I feel like a rebalancing of these stats would improve the game a good amount.
Acceleration, braking, and handling can stay the same.
Downforce, Fuel Eco, and Tire Eco could have their effects boosted so they are useful past the rookie tier.
Cooling and reliability could have the same effect, but boosted a lot so they mean something closer to the end of races. The car parts health could be brought down, but in a way where it takes much more time for it to go to 30% to 29% health than 95% to 94% to allow people a chance to save parts.