I look at the 2821 Cluster sized force as representing only the Bloodnamed 40 of each Clan. There had to be large auxiliary forces made up of those who failed to earn Bloodnames. Without those forces I don't see how they can survive Operation Klondike, much less win it.
the Bloodnamed were more like the officers corps. the auxiliary for each clan (think of the space ship crews alone!) were massive, including technical, medical, military police, engineers, Force Protection. Artillerymen, etc.
Functionally when you count the combat support elements, each "Cluster" was probably two galaxies worth of troops.