I have never understood this line of thinking... you are something like 100 times more likely to be hit by lightening in the US than you are of ever being caught in a mass shooting. By this reasoning you should be walking around with a foil hat with a ground wire taped to the bottom of your shoe.
You could also be caught at a concert where someone is popping off rounds 3000 yards to 4800 yards away. Do you never go to a concert without taking your .338 Laupa mag sniper rifle with you? Why would you go anywhere in public without a sniper rifle?... it has been proven that there is a possibility of of being killed by a mass shooter at greater than hand gun distances... more than once!
It sounds to me from this and the remaining part of the post that you somehow are assuming that engaging at a distance longer than 5 yards somehow necessitates a different type of gun. All it really takes is marksmanship and ability to perform under severe stress. I never suggested that you need to up-gun, and getting to a .338 Lapua example is a gross exaggeration. My Glock 42 is an easy 25 yard gun. If you want to start talking odds, don't bother carrying a gun at all.