Whether the union position on who should be empowered here has merit is orthogonal to the question of whether unions are broadly for expanding or reducing administrative power, no?

Your argument is simplistic and over generalizing... but it is a good example of the ideological battles we see in society. You’d probably find high demand that would justify the hiring of support staff to represent students vs faculty and vs admins in many cases. Whether this expands or decreases an administration is irrelevant. The goal of unionization is a collective voice that is acknowledged.