Did 22 years of low light training on an indoor range with all manner of firearms from .22s to short barreled magnums...I can assure you muzzle flash is a non-issue. From no light to low light to using only flashlights.
We shot both scenarios and exercises and there were zero issues with hitting targets with followup shots...
Theater scenario....38 Super.. The range was dark...what you see is the flash from the camera..
Low light exercises...
Flashlight only...
Bob