Editing MidHammer 40,000 (section)

===Primarchs===
I would suggest a sort of 'Council of Regents', in which they spend a lot of time on Terra, making sure governance is actually competent. They might be Primarchs, but there are only eight of them, and the Imperium is the size of a galaxy. Sure, on occasion they'll venture out to kick ass or inspect the Imperium, but there are so many threats and only so many Primarchs - even they can't be in multiple places at once.
Alternatively, they could be ruling over Segmentums, taking up about as much time - sure, it's a smaller area of space, but now there's only one Primarch.

Ferrus Manus and Fulgrim are BROS FOR LIFE and go on BRO TRIPS OF PURGING TRAITORS AND HIGH ADVENTURE together.

Fulgrim is A GOOD BOY. Horus is THE BEST BOY.

Sanguinus is fabulous hawk boy. Probably gets hit on by everyone who's brave enough.