All of the editors/collectors mentioned in Harker and here mediated their choices of songs, their publication of songs and their theories on the songs and their evolution, but in many different ways, and with some obvious overlap. How we respond to those mediations is surely a pure matter of opinion. Take Bert for example, I don't know of anyone who would say he didn't improve the material he passed on, but the problem for anyone researching is that we don't fully know the extant and the exact details, though it is possible to make informed guesses. In FS in England he mediated in all sorts of ways by overemphasising some aspects of the subject and playing down others. But then all writers do that. I am mediating in writing this post, but no doubt that will be emphasised by the responses to it very shortly.