The lead link of a super circle can set priorities, but it is still up to role fillers to align to them and decide what and how to integrate that.
See letter c for duty to align to circle goals: http://www.holacracy.org/constitution#413
If a person is doing their best to align to priorities, then they may want to request a new hire or additional role filler...or if a LL of a sub circle is not getting enough of the person as a resource, they may want to shop internally or externally for more resources...follow the tension.
It could make sense in my mind for a super circle LL to say prioritize circle A over circle B. In my interpretation, that is fine and it wouldnt have to be a project; it can be a strategy.
But again, it may not be enough to get the resources allocated the way a sub circle LL desires.
In which case, maybe they want an employment level agreement from a highly valuable resource that says Karilen will spend at least 75% of time in "these types of work" and perhaps that could also help.