I'm quite willing to discuss ideas that will make a difference. Banning semi-automatic rifles will most likely not.
The Vegas shooter is the outlier in all of this (the exception-type you keep harping on). And truthfully, while he couldn't do exactly as well as he did (bump stocks being outlawed now) he could still have caused significant loss of life with different weapons. And yes, I do think the average shooter could do just about as well with a handgun - there's not something magical about semi-automatic rifles, especially at not-long-ranges. I'm not sure how you think that statistically I've proven otherwise, but I'd be interested to see how you arrived at that conclusion.
It boils down to the idea of meaningful results. Semi-automatic rifles are used in a small fraction of firearm homicides. If you want to go after them, fine. As I've said I neither own nor intend to own one and don't really care about them one way or another but be honest about only caring about certain types of gun deaths. Beyond even that, there's a couple of problems with banning them. First, there are something like 10 million Ar-15 style firearms out there right now. I'm not sure its even possible to get them all barring a literal door to door search. Second, as I've stated there are plenty of other nearly as efficient ways of killing lots of people.
Its a more complex issue that most realize. Obviously we could do what many other countries have done and essentially ban all guns. I don't think that will fly in America in our lifetimes though so let's ignore that.
One of the problems that many pro-gun people have is that our current laws fail us quite frequently (the Sutherland Springs shooter shouldn't have been allowed to purchase a gun but the Air Force dropped the ball). Why do we think that new laws will be any better? But let's ignore that for now as well.
What I hear most often is about closing the gun show loop hole. On the surface that makes perfect sense, and I would have no objection to requiring any firearm sale of any kind requiring a background check. Adam Lanza stole his mother's guns. A universal background check wouldn't have stopped him (I am not opposed to the idea, just pointing out that it won't stop all mass shootings) Another issue, and a more common one than you'd think, is within families. Barring a universal registration of all firearms in America (which would be a hard sell), you'll have problems with that. For example, I have 3 generations of guns in my safe - my grandfathers', father's, and my own. The government knows about the 1 rifle that was bought in my name, the others it does not. If I choose to give them to other family down the road, there will be no record of that.