Of course the marginal paper is a thing. If there were marginally less research funding, the research program cancelled wouldn't be chosen at random, it would be the least promising one. We can't be sure ex ante that that would be the least successful paper, but given that most fields have 20% or more of papers getting no citations at all, and other studies show that papers with very low citation counts are usually being cited by the same author, that's good evidence.

Note that I did not say that papers, on average, get no citations. I said that the average (I.e. median) paper gets no citations.