To me it seems the FBI does not really look for the brightest. Rather, they want a certain personality type that seeks conformity in groups and group identity, and will mold oneself to the organization and its very tight bureaucracy and culture.
That policy was set by the cross dressing Edgar Hoover. Easier to mold mush minds from the Ivy League than hardened soldiers.
The FBI just wants clay heads to fill the desk.
Ahhh I recognize this from a business class , It’s the German employment philosophy of the 1930’s.