You did a poor job of summing up.
I think that most folks here like to plan for for the worst case scenario, with the knowledge that it's a lot easier to adjust to a less severe threat, than spool up to meet one that is more dangerous than previously anticipated.
So a shotgun is not enough for a worst case scenario and your assertion is that you need a bedside AR to TRULY be prepared?
Blindly ramping up the "worst case scenario" without any logic isn't being more prepared, it's just being retarded.
What if they have hand grenades and high explosives? Clearly you are just paying it lip service unless you dig a fighting hole with a sump. I hope you have the range card for your house and yard filled out and it will take some effort...but unless you register the FPF you can't truly be safe either.
I own a 6.8mm AR (among others) and no shotgun, and after this thread I feel like going out to buy a new 870...blah.