doing something at the expense of something

1. Does the following paragraph say "Both he and they have been condemned for doing X at the expense of Y? Does Y also refer to "Bourriaud and his artists"?

2. What does "posing searching questions relating to" imply?

3. How can the meaning of the highlighted section of the text relate to the meaning of the first part of it?

Context:

As a curator, Bourriaud evidently has a stable of ‘exemplary artists’ and collaborators, many of whom he cites in his book. Both he and they have been rightly taken to task – in a protracted debate spread over the pages of several journals– for developing a theory and practice that prioritises too vaguely or, indeed, ‘mistakenly’ the notions of continuous open-endedness and viewer participation, at the expense of posing searching questions relating to the actual nature and outcome of the dialogical relations they would seek in such encounters between spectator, location and work. Thus, as Claire Bishop argues forcefully in her article ‘Antagonism and Relational Aesthetics’, Deutsche’s important emphasis, referred to earlier, on democracy coming about where ‘relations of conflict are sustained, not aroused’, threatens to become dissipated. Instead, using the work of Thomas Hirschhorn as indicative, Bishop concludes: ‘The tasks facing us today are to analyse how contemporary art addresses the viewer and to assess the quality of the audience relations it produces: the subject position that any work presupposes and the democratic notions it upholds, and how these are manifested in our experience of the work’.
Interestingly, Bishop’s critique as a whole is premised here effectively on the (antagonistic) opposition of two pairs of artists, the couple whose work she champions, literally for their ‘better democracy’, emerging as having a ‘tougher, more disruptive approach to “relations”’.