Looking at it from the other side, it's not really fair for those schools in the high 400's/low 500's range to play against schools who are twice (a couple almost triple) their size and who are pulling kids from Canada and other states.
MBA, McCallie, CBHS, MUS all have more boys in their school than some of the schools you lumped in have students.
If you want those schools to play up, you have to have the same opinion for the lower division as well. There should be two in that scenario. You can't care for the schools with the really low numbers, but not care about the schools with the middle of the road numbers.
And remember, the number was set by two schools who did not want to play up in the AAA division in the first place and had members of the BOC.