I thought whole point of that setting is that literally everyone is sacrificed to war, regardless of the side. Space marines are one in a million combatants at best, just like how chaos has one cool demon for every jillion little bullshit mobs.
Honestly the only good faction to be in is Orks, because while they all die horribly in war, they're genetically engineered to FUCKING LOVE IT! It's their favorite thing ever being ripped apart in bloody combat!