Would Oldster as the second armed person in the theater make it worse?

From my point of view, yeah, I think it would.

Holmes was covered head to toe in body armor, including extra protection for his throat.

Would olddude have shot anyway with his daughter in peril. Probably yeah.

Would he have angered the gunman enough to draw his attention and get half the rifle clip emptied into him. and those in the neighboring seats. Probably yeah. We'd all have missed you Dan.

If you don't have a clean, armor piercing, kill shot do you have any business taking out a gun?

In a perfect NRA world, half the people in the theater would have been packing armor piercing ammo in their guns which would have to pack enough punch for a clean kill.

In that world all the nutjob would have to do is toss his smoke bombs and a few fire crackers and let the vigilante nutjobs kill each other.