By grew out of, I mean it's the upgrade thing has been done in loads of racing games and is tired by this point to me I have no interest in doing stuff like that anymore. And as for stat changer it basically is, here is part of the game preview article on PCGAMER .COM
" This also means you can take a favourite car all the way through a career, from the lowest level to high-end events, increasing its performance index with new parts. Developer Slightly Mad Studios wants players to feel like they're constantly improving and making progress, and playing in any mode, including multiplayer, will earn you experience points and in-game currency."
As for them saying handling differences and performance feeling radically different etc with upgrades, well they also said "all the sim you could want" then removed pit stops, wear etc.
I wouldn't hold your breath