Holacracy Community of Practice Archive, 2015-2019 Community Holacracy Web Site

The experience I've had is that since the Lead Link holds the role of the circle...the super circle created a role that became a circle and the LL holds that role. The super circle articulate the purpose (raison d'etre) for that circle, and that is used to prioritize the output of that circle. Given that the LL is fully accountable for all outcomes of that circle on behalf of the Super Circle, it functions pretty well to have them hold the functional responsibility of prioritization. 
In practice, prioritization is held by the people doing the work until their work is no longer fulfilling the purpose of the circle (the LL's purpose). Once a role is not delivering what is expected, the LL takes a more active role in that roles outputs...which often includes prioritization.