Pretty sure that isn't true, given that all we know from the text is that the world of Macragge had maintained contact with its neighboring systems, its industries and peoples having largely survived the chaos of the Age of Strife. However it still had large rebel, uncivilized populations such as the Illyrians. As well as we know that Konor, Roboute's adoptive father, won his fame from pacifying a continent. He's a Caesar figure, and Roboute is the Octavian. Now we look at Espandor. It was there that the Emperor heard stories of the extraordinary son of Consul Konor, and realized that he had found one of the lost Primarchs. The Emperor was off course for five years due to a warp storm, and when he reached Macragge, Roboute had been ruling roughly for that time due to a coup that had destroyed the planet's capital city and had killed his father. He reformed the entire civil social strata, and made it more prosperous then ever, engaging in trade with several star systems. It is presumed that this trade already existed, but Roboute being such a good administrator was able to convene these systems into the foundation of Ultramar. Espandor was one of these systems, as they were reformed into the realm of Ultramar with the reorganization, and would commit recruits and resources to the Ultramarines.
Now, I am not doubting that Roboute might have had designs to conquer or subsume these neighboring realms, but those within the Inwit Cluster, from my understanding, had already largely conquered the neighboring systems. They had been exacting tribute from them and the entire atmosphere of Inwit beamed with starships and orbital arrays, while the scions of the clans still lived as they always had, within the desolate wasteland of their home planet, as they thought it brought them strength. Dorn like I said was able to meet the Emperor at the head of an entire fleet, which is more then what any other Primarch ever seemed capable of. Rogal was also ruling his system for anywhere up to 40 years, and was found 7th to Roboute's 8th.
It's a toss up in my opinion. But again, semantics for the sake of argumentation. Shouldn't inflect anything on the game if all the starts will be symmetrical with a sector each.