Flashback to the 1970s!
It looks like that Carrol is bringing us back to the old debates concerning strcuturalist versus instrumentalist views of the state: Poulantzas (who was a disciple of Althusser) versus, say, Ralph Milliband or, indeed, Domhoff. I, myself, think that I am inclined towards the take that Richard W. Miller took in his book, "Analyzing Marx", called for a synthesis of the structuralist and instrumentalist views of the state.
^^^^ CB: It defies common sense to think that the capitalist ruling class has without class consciousness and a high level of class unity won the Cold War and retained dominance of the states of the imperialist power nations over the last 100 years in the face of conscious, Marxist led working class challenges. There is all kinds of evidence that the ruling class is centralized.
As to the term "agent", the ruling class is the "principle". It has lots of "agents". A principle directs and agent. A principle is the subject. This is the legal use of "principle/agent" ( See the law of agency). Post modernists or whoever have given the term "agent" the opposite meaning from this legal meaning.