An unformed thought:
I’m thinking that a key move for Latour may simply have been to differentiate agency from being. That would allow him to put all beings on the same ontological footing while at the same time acknowledging that different kinds of beings have different powers of agency.
Such differentiation stands in radical contrast to the traditional Great Chain of Being where higher beings also had more powers (agency). In the Great Chain being and agency are the same thing.
What about non-reduction? Could it be that non-reduction forces a distinction between being and agency?