Where are the Sisters of Battle in this discussion? I get that in almost all of the work that isn't about their gory death, they show up as the hoodwinked minions of Imperial corruption, but when they aren't written as a direct foil to the free-thinking modernist-derived protagonist they're an outstanding force for the future of humanity. Literally the conviction to deny chaos and shape the warp to aid them. And they might be wearing power armour, but they're still baseline human inside. They handle the darker secrets of the universe, and they don't fall prey to ambition and corruption nearly as much as space marines. If SoB became the standard, the Imperium could hold. We all know the general lore and each side can argue the battles fought, so I'll only mention their most arduous task. The SoB staff the black ships, upon whose twisted cargo the Imperium relies for FTL communication and the preservation of the Emperor. Regular guardsmen can't handle it, and SM are to rare to be tasked with it. And yes, SoB are overly zealous religious nuts. The Imperium tried secular once, ended in the Horus Heresy and the Emps dying. To make it in 40k, you need some crazy faith power.
