He definitely could have done lots of damage with a couple handguns (see VA shooter) and/or shotguns.So if this idiot didn't have access to the type of weapons he had, what would he have done to cause the chaos he did? Because I don't think he would have been deterred.
But not nearly as much damage as with the AR 15 and he would have put himself at more risk for injury/capture with the previously mentioned weapons.
Of course, he could have just used a uhaul full of explosives but that wouldn't have been as exciting for him I think.