No, I don’t think it’s underpopulated at all. Im also pretty sure that the handful of Special Class investigators we’ve seen is all the Special Class investigators there are.
We’ve been told that even becoming a First Class would take an investigator 10 years at the very minimum, and that’s considered to be a very speedy, swift promotion that requires not insignificant talent to achieve. And most people don’t move past that even if they do achieve it.
Many investigators start at Rank 2 after graduating the Academy, get promoted to Rank 1 and stay there for the rest of their careers. Nothing to be ashamed of, there’s a lot of people in any army, not everyone’s a colonel. And CCG is at its heart a military force.
You have to also remember that – yeah, due to constraints of narrative space and time, – we’ve only seen the best and brightest, because what fun would it be to mull about with Rank 3 investigators (of which there are probably dozens, if not hundreds) for the whole manga? And there can only be a handful of best and brightest in any field.
To see just how good and bright they are, please consider this: when Ishida wrote CCG guidelines slash comparative analysis on how many investigators it would take to change a lightbulb, it was:
- against an A rank ghoul: one First Class investigator.
- against an S- rank ghoul: several Associate Special Class investigators and their squads comprised of investigators of any class and rank.
- against an S+ rank ghoul: several Special Class investigators and their squads comprised of talented investigators of any class and rank.
- against an SS rank ghoul: many Special Class investigators and their squads.
This isn’t untrue, we’ve seen how many people died trying to capture Yoshimura and Eto, Houji alluded to dozens of investigators dying during the Chi She Lian operation, etc etc. So far, everyone we’ve seen has been grossly overperforming imo. By official CCG guidelines, Hirako should be able to take on, like, Torso. Meanwhile Suzuya’s squad just single-handedly defeated Kurona, who has to be at least a tentative S+ at this point (a ghoul’s rank is tied to their perceived danger to humans, not raw strength per se).