The CM indeed posted this. I do not know the data sheet, but he said "single digit percentage". That said, he did not say who qualifies to be a "raider".
Given how this was used in the community, it is everyone that plays instances. IMO it was people interested only in the hardest content and things like server firsts.
The old CM was playing divide and conquer. IMO not a good idea, as too many player groups depend on each other, even if they don't see it. With the least common factor being the shared cost of servers and common development.