"The [assault rifle] bullet is going through multiple walls. You are far more likely to kill a family member before killing the intruder. A shotgun and a 9mm pistol are far more useful."

Sure, a .223 Rem round can still be lethal after going through a bunch of interior walls.

However, a 9mm hollow point, after going through 10 sheets of of 1/2" drywall (5 interior walls), is still able to penetrate 9" into a block of ballistic gelatin (i.e. still lethal).

https://youtu.be/X0qgQoej5zE?t=68