Malal (npub1gp3…ttkk) people misunderstand the odds are so against the SW universe. They're against the Imperium who cares too little of the lives they throw away. The Galactic Empire and Republic care too much for the lives of their soldiers, but the Imperium see it as dying in the name of the God Emperor.
Then you throw in a Primarch, like Leman Russ, they're just fucked. Then you imagine a scenario, one lone Zealot carving a path of destruction with a chainsword and a bolter. The surrendering will start when they witness one of their comrades be reduced to a pair of legs by an oversized pistol.