When we say an author is influential, that means we are saying that those influenced by him or her are significant in some way. In other words, if we say Beckett is influential, and then give a list of playwrights to prove our case (Albee, Pinter, Mamet, Ionesco), we are really saying that these are writers of some importance. (Otherwises there would be no special value in being influential. ) So when we say that WCW is influential, it is because of Creeley, Snyder, O'Hara, and other similarly "influential" poets. Thus it makes no sense to speak of influence in quantitative terms, to speak of how many writers are influenced by a particular figure. The literature we truly value is always less than one percent of the total literature that exists, is published. If someone said a playwright named "Snow" was more influential, because he had influenced "Rain, Sleet, and Fog" and a hundred more that I've never heard of, I would say that is another conversation.