[@BCTheEntity] Well, when reading about the Emperor, the Primarchs always less of "Sons" and more "A means to an end" with the exception of Horus, who he really did love as a son. Looking at old Empy's actions, my understanding of it was that he would use the Primarchs and the Legions to conquer the galaxy, then probably have them wiped out when everything was 100% secured, like he did with the Thunder Warriors. As such, the idea behind Rumisklinese was that the Emperor would allow him to live with that helmet, so long as nobody found out what was underneath. This is due to his Gene-seed being unmutated.

That being said, although I think Rumisklinese would be the more compelling character, I think Ruubai would be easier for interaction with the rest of the universe.