Well ya, but how much of that is a ship or asteroid that they can inhabit, and how much of that is empty space? That is the real question.

The reef is based off the real asteroid belt we have in our system. It's huge. There are asteroids there that are almost planets. In the Grimoire the Reef Cryptarchy have a giant hollowed out asteroid as their library/archive. A huge chunk of their population was killed on Pallas but there were an unknown number of golden age stations/colonies in the asteroid belt pre-collapse. I'd say the awoken are still populous, but their fleet is significantly weakened.