ACman said:
Military/paramilitary/intelligence and associated services then. The interesting bit is the Adeptus Administratum who seem to control planets and military. and in the back-ground even they sound like inhuman monks.
Supposedly this system of governance has been going controlling the entire human galaxy for 10,000 years; which sounds like a situation where you'd have sections of the administratum fall under the control of local princes al la europe after the Roman Empire. But no, the empire is stable despite constant war.
Hence I think it would be more interesting for the empire to fragment. Hence my previous Catholic/Protestant/Orthodox analogy.
The Administratum is also everything civil matters. Infrastructure, civil services, health care that sort of thing. It's a really broad umbrella, and another reason why your chart isn't that good at describing how the society functions.
For an example, the military branch of the administratum is a section in itself, called the munitorium. While I concede war and a militaristic mindset is weaved closely into the societys structure, it is a necessity born out of constant conflict. On any number of fronts.
The empire can't fragment. If it were ever to cease functioning as it does now, humanity would perish. Which would not make it very interesting at all, since it would mean the end of the setting.
Yes. There is only war. Not as in every planet is constantly engulfed in strife, but humanity as a whole is at constant conflict, and it is barely holding. If it were to become divisioned, if the warmachine was not fed, it would falter in its defense. And if the public was not constantly scrutinized for signs of heresy, it would crumble from within. Not because not being a fervant churchgoer is a bad thing, but because chaos must be held at bay at all costs.