Here's my perspective: the purpose of any cultural policy or regulation should be to encourage a diversity of both participation and works (that is: more people making art, and more kinds of art being made).Paley & Doctorow argue over Non-Commercial licenses
ISTM that your assertion amounts to: "Whatever forms of participation that come into existence as a result of the capitalization opportunities that accrue in an exclusive rights regime, they are dwarfed by the works that lurk in potentia should such a regime perish."
IOW: we unequivocally get *some* participation in culture as a result of exclusive rights regimes, some of which would not exist except for exclusive rights. You believe that if this regime and the works that depend on it was to vanish, the new works that would come into existence as a result would offset the losses.
I don't know how either assertion could be tested. We both have firsthand experience of both modes of creativity -- I know of works that wouldn't have been capitalized absent the higher returns expected in the presence of exclusive rights; I also know of works that could only have been made in their absence.