Joe, I don't think "performer" is all that relevant to folk songs that were sung in people's homes, or other setting. I figure "mediator" is someone who can, and does, decide what to share with other people. This isn't necessarily bad, as collectors have to limit the scope of their collecting somehow. Sometimes, it's about what type of song to include, sometimes it's a selection of versions, or verses. Any collector isn't the only one around.