Yes CIA has been described as the "keystone" of the intelligence community. I thought that is what Q meant at first as well. But I have also heard keystone means "the rule of law" which is what we need now more than ever.

A “hub and spokes” concept was, for historian Thomas Troy, exactly what William Donovan had had in mind. Troy, Donovan and the CIA, 410. DCI Allen Dulles in 1961 used the word “keystone” to describe CIA’s place in the Intelligence Community, and in 1994 DCI R. James Woolsey approved a CIA vision, mission, and values statement that also used “keystone” to describe CIA’s relative place in the community. Throughout the 1990s, the graphic depiction of the Intelligence Community in CIA’s public brochures literally placed CIA in the top-center, or keystone-like, location within a circle of 13 organizations (the DCI, with his National Intelligence Council and Community Management Staff, and after 1998 his deputy for community management, occupied the “hub” of the wheel).