Prove my argument wrong then. I claimed ease of reload is the only actual advantage the AR has. Which is exactly what you just wrote.
If I have to shoot my targets 5 times with an AR to kill/incapacitate them but only once with a shotgun, I have the potential to do at least as much damage as the AR in a similar time frame.
I'm not trying to say a shotgun is BETTER at killing people than an AR, just that it's not necessarily or substantially WORSE. In a war zone, with hard cover, accuracy, and distance to take into consideration of course the AR is superior, but when discussing mass shooting scenarios it's simply not true that an AR will always be better at killing people than other types of weapons. There are just too many variables.