Somehow multiple BoS members in T-51b got killed in The Glow, despite the only threats present being armed with assault rifles, sniper rifles and the occasional shotgun.
Maybe the robots with supernatural accuracy targeted the joints? It mentions somebody's arm flew off with burning flesh, maybe a plasma hit?
The Ancient Brotherhood Holodisk also mentioned that they were cut to ribbons and had never seen weapons cut through armor like that. Which would make little sense unless assault rifles, sniper rifles and the occasional shotgun are weapons military soldiers have never encountered before.
It's more telling that you can see in the wall lockers on the fifth/last level are an array of plasma and pulse grenades as well as laser and plasma weapons, and miniguns and rocket launchers/missiles etc.
So while the gameplay might show one thing, the lore from the holodisk could indicate otherwise.