>a functionally equivalent semi-auto hunting rifle has exactly the same destructive power).

I'd strongly argue against this point. Most hunting rifles have 5 round mags (legal limit for hunting in a lot of places). They won't accept 30 round mags. They're also chambered in more powerful calibers which have much more recoil.

An active shooter with his dad's hunting rifle is much less dangerous than the same shooter with an AR-15 with 30 round mags.