The hypotheticals are just that, IF he had a gun, yes, more might have been killed. If someone else present had a gun, maybe fewer would have been killed.
But we live in a country where firearms are prevalent, and that isn't going to change no matter the hypotheticals. I noticed the Administration is trying to close the so called gun show loophole, which basically is a fabrication that doesn't exist, but it SOUNDS good, to folks who never attended a gun show.
The new rules are so vague nobody will pay much attention to them, much less of course criminals.