I would be careful about just an effective SD argument.
In our own discussions, many have claimed you don't need XY or Z level of firepower for most effective SD.
One could claim that most of us could effective defend the homestead with a SW Model 10 and a pump shotgun. In fact, if I weren't me - those two guns with modern SD ammo would do just fine in the vast majority of cases.
So are we limited to that?