The Vilani of the Ziru Sirka were culturally stagnant, but that is in complete contrast to how the Vilani were before, and probably during, the consolidation wars.
The Vilani were explorers, they used STL ships for 590 years to build colonies and encountered another human race plus a few alien races during this period.
They then invented their jump drive and for the next 2920 years or so built up colony worlds, explored, traded and were the umbrella hegemony for the whole of the space they colonised and traded with. They also went from TL9 to TL10 and then finally achieved TL11.
They then became militaristic and demanded their hegemony become overt rulership, hence the consolidation wars that lasted just over a thousand years (1030). For some reason they didn't push to TL12 (I have a theory for that).
Only now would the Ziru Sirka stagnate and deliberately and culturally restrict innovation and progress. Twelve hundred years of Empire would see the beginning of the end when the Intersteller Wars era blew up upon encountering the Terrans.
The Vilani had nearly five thousand seven hundred years of colony building and empire to populate this small piece of the galaxy, there would be some mixing with other human minor races no doubt, but I would estimate the population of the Ziru Sirka to be hundreds of trillions.
Now the Rule of Man lasted just over three hundred years, during that time there was some migration of Terrans into the Ziru Sirka. Canon tells us the population of Earth at the start of the ISW was twelve billion.
How many of that twelve billion would migrate into the Ziru Sirka? Let's go with the preposterous figure of one billion migrants.
One billion added to a hundred trillion. One per one hundred thousand.