I think the amazing thing about Rivera, like Hoffman and a very few others, is longevity. So many closers come and go, surviving for a while on their unfamiliarity with each of the hitters. For most of them though, once the hitters have seen them a few times, the jig is up.
Not sure what this does to help rank Rivera as a Yankee, but it does, I think, point to the fact that he was not just a closer. At his job in baseball, he was dominant for a decade.