I'm calling trick question!
How about this: there are no "worst cars" of the game. It just doesn't make sense. Why would they go through all the trouble of building cars for such a major EA title if they sucked in every form of race in the game? Every car has to be good for at least one race mode. Maybe you can't beat Ryu with it but you should be able to get through enough of the game to unlock the kings with it.
Though in the end it all depends on the player to utilize a cars potential.
Wrong. If that's the case, then you try using a Civic Si to beat Ryo. You try dominating online in a AE86. Prove it and I'll take back this remark.
Moving on....