I personally like the Dark Forest Imperium.

what is the dark forest imperium? Its taking the Imperiums millions worlds across the galaxy and superimposing it on the real life milky way. Even if the Imperium composes 5 million systems. It would only comprise of 0.002% of the current star systems in the galaxy.
But I like the idea of the Imperium maintaining this appearance of hegemony, but in reality there's things lurking out there. I liken it to the empire in the old world, where you have cities, but they're surrounded by dark forest filled with beastmen and goblins.