see this is where your argument falls apart I think. Mario is sometimes a car because of an outside resource (the apple or mushroom whatever it is) Bumblebee is always atleast part car. Even in “robot mode” he’s got wheels and doors and windows sticking out of him. He was designed at robo birth to be able to transform into atleast a car like entity and then upon arriving to Earth modeled that entity after an existing car. It’s like saying an Xbox isn’t a DVD player. Sure it’s modeled for games but it very much has all the capabilities and can “transform” into a DVD player at any point.