Joe: The raw RGB video of the home and MVS systems are the same, it's what happens when the RGB is converted to something else that affects the video quality. Most will tell you MVS video is superior, which isn't strictly true, it's just that the aftermarket video encoders are generally higher quality than a home system. In your case, the MVS you borrowed probably had an inferior video encoder.
As far as stereo, most MVS boards were stereo. However, Jamma standard is mono, so the one you borrowed was either A: Hooked to a mono only supergun, B: A mono one slot board or C: Lazy consolizer didn't hook up both L and R channels.