I invite anyone who thinks 6 shot from a 20 gauge at 10 feet is not a viable defense round to stand in front of one.
That is pretty big talk considering nobody has suggested 6 shots from a 20 gauge at 10 feet isn't viable defense.
Being "viable defense" and being a reliable stopper are not the same thing. Besides, what in the world makes you think you would get a chance to fire all six shots? If you want to based defense on the cumulative effects of repeated shots, then a Daisy Red Rider BB gun can be a viable defense as well.
And I bet you aren't willing to stand in front of one to be shot multiple times either, so then obviously the Red Rider is every bit as good of a reliable defense as you 20 ga. shotgun, right?
Silly and stupid criteria give you silly and stupid results.
Challenging folks to stand in front of a weapon and letting them be hit with it is not a valid challenge to substantiate the viability of that weapon for self defense.