User blog comment:Algrim Whitefang/Fall of Cadia - Gathering Storm III: Rise of The Primarch/@comment-8881468-20170204102440/@comment-8881468-20170207034206

I'd actually have to read the thread again to give a more detailed reply. I guess that was one in terms of the heresy and guilliman writing up the codex to combine the different units from various Legions into a fighting force (which was imo handled well vi the codex and the red marked and so on stories.

Looking at the primarchs as a whole, Guilliman is the effective administrator and leader but not a figure of "public function or "flamboyance" --> hence also Emperor Sanguinius.

However: There is still the problem of the Imperium having drasticcally changed and Institutions having become very entrenched that were unforseeable by Guilliman (f.e. the Inquisition or the Ministorum)