ATN082268 I think you are mixing what a 12ga. shotgun is capable of in theory vs. reality. No a single pull of the trigger of a 5.56 AR style firearm will not throw as much lead downrange as a 12ga. load of 00 buck. However the AR has less recoil which means that for someone who is say 5'0" and 115lb soaking wet, it is more appealing to train with. Which experience has shown is the difference when it comes to home defense duty. If the defender has a 12ga. but they don't like to practice with it because of the recoil/weight/difference in reloading/sound/ergonomics, it is no more useful than a golf club.
For someone buying a gun for their home defense that doesn't have experience with firearms, an AR15 platform is usually a better bet. Take that person to the range for an afternoon with an AR15 and a 12ga. and then put them through a realistic course of fire based around home defense at the end and I guarantee you that they will perform much better with the AR and feel much more confident in themselves with it. Unless they REALLY like shotguns.
My apologies as I don't want to derail this thread, but do a search on this site of all the threads about home defense, shotgun for HD, HD shotgun, HD weapon, and you will begin to see a trend. Experienced forum members with real life training, simulated training, and years of experience will say that it's the mindset/skillset that matters most. What gun will allow you to obtain that skillset: 12ga. or AR15? That's up to you.