I think that is the biggest argument towards using a tuple: that just setting the priority is not enough (and also is decontextualized as different policies have different priorities). On the other hand one could say that the API is a low level API and therefore the user should be aware of such a problem. Also, using a tuple makes the API a bit asymmetric as Serhiy mention but I think this can compensate for the conceptual map the will be established (as in each priority is associated with a policy) if the tuple API is used.