Your all wrong, here is why.
The standard type of crossed Universal Joint, like you see at the end of a driveshaft near the rear differential on a full size pickup, is called a Cardan joint. If a single Cardan joint is used on a drive axle and the axle runs at an angle, then the axle actually accelerates and decelerates four time per revolution. On a pickup this vibration is taken up by a second single Cardan Joint near the output shaft of the transmission. If the output shaft angle of the transmission and differential input shaft angle are close to the same, which they are from the factory, then the two Cardan joints exactly cancel their vibrations. On an RC car, this small change in the rotational movement of the drive axles (vibration) is usually taken up by motion of the ball differential which transmits the motion to the axle on the other side and to the driveline. This does a good job of dissipating the excess vibration, especially if you have a belt drive. When you run a the car on a stand the vibration becomes a big problem. The diff no longer absorbs the vibration and the inner dogbone pin rocks back and forth in the drive cup slot. If your tires were out of ballance the car would vibrate just the same when the wheels are strait.
I am smarter than all of you combined!