Well I’m more talking about how multiple campaigns had fighting numbers in the 30000s to (rarely and debateable)40000 at peak. Vassal forces that often included Slavs,Armenians Lombards, Hungarians Turks, Crusaders should also be taken into account, a good example being the battle of Myriokephalon. Could also include the Akritoi who would cover the advance of main Armies. 20000 support crew is definitely exaggeration I’ve read like 5000 at most.
Also that’s sounds like the definition of centralization to me(under the Emperor) plus the Domestic actled like the Commander in Chief he didn’t rule over multiple themes, often just leading campaigns in the Emperors Name. Plus I’m pretty sure most Duxs didn’t lead multiple themes and there was also the Katepans.
It's been a while. I might be lumping the feodorati in with the support in my number of "not Byzantine soldiers" number. If so, it seems we're not that far apart.
The English army at agincourt 1415 may have been completely men at arms in game terms:
https://www.futurelearn.com/courses/agincourt/0/steps/8842
And England during this time was a rather weak 3-4 million population kingdom, Byzantine Empire had a much larger population on its height and thus more resources.
For most of the early CK2 period, the empire had 8-10 million subjects. It might have had as many as 13M during its peak in the early 11th century, plunging to around 6 soon after Manzikert.
However, raw population doesn't tell you how organized a particular state was. Economic development, centralization, infrastructure and culture all play bigger roles.
Most crucial of all is what, exactly, you're using your army for in the first place. When the Romans were outnumbeded by the Arabs 4:1 and we're receiving annual raids by the Caliphate, they relied much more heavily on levy-like conscripts.
Later on, the armies of reconquest headed by Nicephorus Phokas and John Tzimiskes were almost entirely tagmata, since they relied much more on cavalry operations (backed by heavy infantry) in the Levant.
