We have had a good amount of playtesters and that is not one of the complaints we've had, we give the hint as to the fact you can shoot the gun to see, as i said other people tried the game and even finished it.
We also included cheats so everyone can finish it.... just use those and use the gun more. The theme of the jam is darkness adding a spotlight/flashlight would make it generic, there would be nothing to do in the game aside from following lights shooting enemies and runes, this way navigating and finding your way is also part of the experience.
I have noticed most games of the jam it is merely dark and you can still see which in my opinion makes it pointless, decreased visibility doesn't work, visibility is something you either have or you don't, according to range.
The crystals were supposed to give out a bit more light you are correct there. Try the game again and actually use the gun since its the main mechanic.