[TomGuy]

Had it not been for his guns, he would have used a bomb. That would have killed hundreds.

I never heard a report of the occupancy number of the apartment building where the perp lived. But, it is a 3-story building. Per police reports, had the explosives in his apartment gone off, they would probably have demolished the entire building. Considering the time of night, such as explosion could have resulted in a higher death toll than the shooting at the theater.

[Dutch Boy]

Both places would have had massive deaths that would likely dwarf his shooting deaths. This guy was on a mission. He luckily chose guns over bombs. Bombs would have been far worse.

[Trailerpark Badass]

Per police reports, had the explosives in his apartment gone off, they would probably have demolished the entire building.

Has there been any proof he had explosives?

The video of the destruction of the "devices" show fireballs, likely from gasoline or some other incendiary material. I think it is extremely unlikely he had any material that could be properly labelled "explosives."