The AR Series from it's inception was designed as a combat weapon, there is not much to dispute about that. Yes, over the years, it has been re-chambered to handle various rounds and calibers, some good for hunting, but the most common (civilian) chambering is for the .223 Remington, which is inferior to, say, the Win. 30-30 when stalking the willy white-tail in heavily timbered terrain, IMHO.
I don't know what professionals you are citing, but people that I know, who have direct intimate knowledge on the subject, maintain that a buckshot (not bird shot) round in a 12 gauge is simply horrendously lethal at in-door or in-house ranges with little chance of collateral injury from wall penetration. For me, anyway, that would be my choice, if needed.
And yes, many types of non-military auto-loaders have been around for decades. But, I still say no one needs a 30 round mag. Not unless you plan on killing lots of people.
We disagree on the training. How many rounds do you fire in a month? Or a year? At what range and at what targets? More than I, perhaps, but practice, especially tactical practice is invaluable if you do feel threatened.
Granted, need is not a requirement. Happily, I have never felt the "need" to have a carry-weapon for protection. I have always been a target shooter, so no real need there. I was attempting to address the apologists who believe that everyone should be armed at all times. I know a few folks ("rude toters"... I might have to steal that phrase if you don't mind) who, though not mentally ill, legally carry a weapon that they probably should not have. Again, my humble opinion.
Oh, and by the way, your linked post was excellent.