Yeah, it gets pretty ridiculous at times. My favorite is when the game stops even trying to hide the CPU assistance/rubber-band and you see shit like your AI opponents' speed suddenly double. As much as I love Jam for the multiplayer with friends, the gold and diamond challenges have almost brought me to the point of spiking my controller on the floor a few times. There was one I actually gave up on and will never even try again.
Artificial difficulty pisses me off. Whoever worked on the AI deserves a cock punch that is so hard and so direct that their gonads rupture on impact.