As for the rest, Demons are very well capable of crafting civilizations for themselves, despite Fels destructive influence.
Their societal structures are obviously prone to.... well, chaos, war and mayhem, but we know of demonic societies and have interacted with moderate/independent demons already.
Sure, their planets would be largely destroyed or wastelands like Argus, but as we can clearly tell that doesn't really mean much to the Demons inhabiting those places.
They either don't care or thrive in them.
Same for the Void, which also can form and maintain civilizations.
The Black Empire was exactly that, and we might not like how it conducted itself but from what we can tell the Aqir and the Old Gods thrived during those times too.
Even the Void Ethereals, despite how insane most of them are, they do manage to organize and live in their Void infused states.