I think the drivers are mostly balanced. Some cars obviously excel at different rounds. Slow cars have issues with checkpoint races, but can easily dominate the car wreck rounds.
Natalya has the strongest car in the game. Pick a loadout with the engine upgrade and impact increase and she's even more powerful. You can just ram the other cars and win. You don't even need to use weapons when destroying other cars. She doesn't need a high damage special at all.
"You're just not ready for me."-Excella "Those who want everything will end up with nothing."--Lulu, FFX