I agree with your points about the over-emphasis on principle-agent types of governance arrangements. The Cornforth (2004) article reoriented my thinking (thank you). I recognized that it was not "P-A" I was critiquing, but the unitarist tradition. That approach helped with definitional rigor
Furthermore, there is no discussion of principal-agent literature in a third sector context (see, for example, Jegers, 2009), which is quite surprising since the proposition to go beyond the traditional principal-agent literature is one of the main ideas of the manuscript.