I agree with your critique. I have adjusted accordingly. I did this by separating the co-operative model from the third sector, and instead noted that there exists commonalities which allows for comparative learning and innovations in governance.
The characterisation of third sector governance is too crude. For example, the third sector itself can be seen as diverse with philanthropic, mutual, cooperative and association sub-sectors. The comments at the start of the literature review might apply to foundations and charities, but are less true of association and mutuals (let alone cooperatives). Also, where there are accounting regulations (like SORP), there are mechanism that keep associations and charities accountable to their donors.