A Novice has a much better shot of doing mass damage with a Shot gun and some Buck shot, than with an Assault Rifle.
You are incorrect. Real world shows novices and new shooters hit more readily and controlled with a 5.56 carbine. Time and time again. Especially after the first round is fired.
Are you talking about range shooting or home defense situations? I wonder if there are even any accurate statistics about that kind of thing to be found anywhere.
I would think the point is more that a novice is more likely to hit, and hopefully stop, an intruder with the shotgun and buckshot than a rifle or pistol because of the spread. It's not really about the weapon but the ammo. You may be able to get buckshot rounds for other types of firearms than shotguns, but that's the more common weapon to think of.
I'm not in favor of the assault weapons ban, but I can understand saying a shotgun is a better home defense weapon.