If the guy was spray firing back and forth, there would be a brief pause at the end of each sweep that could have sent several bullets on near-identical trajectories. I don’t see anything here that screams “the perp could not have made those shots” - because he was not engaging in marksmanship, he was spray firing at fish in a barrel, which takes some endurance and some practice but not a lot of skill, IMO, and since he had lots of guns he didn’t care if he jammed a gun each minute or two. He would have just grabbed another, and the sheriff said some of the guns had jammed.
I will be very surprised if it turns out that any victims were hit by multiple gunshots. Maybe one, on a fluke, but no more than that.