I shoot a lot, typically 200 rounds a day, seven days a week, both rifle and pistol. I am an extremely good shot, but I would not have been able to hit him shooting 300 feet up and from far enough away to get a good angle, not even one shot in ten with any pistol I own. How many people would have had access to a rifle? It's Vegas, not deer hunting country. In the Texas Tower shooting, lost of people had rifles to shoot back, but that was 50 years ago and in Texas.
Dan Bilzerian was there and a girl next to him was shot in the head so he ran to his truck to get a rifle (he usually has 100k worth of the best gear money can buy in his vehicle and far better than anything the SWAT team has). I think at that point the police told him to leave.
By my calculation you spend around four thousand dollars a month just on ammo alone. You must be a very wealthy man.