I'm not really sure you can avoid 'putting your stamp' on music.

Is such a thing to be avoided.
Someone like Brian, shows his passion and commitment for a piece - its obviously important to him that he imparts to his audience what it is that moved him and inspired his interest.

Surely this isn't a negative thing. admittedly the source singer never had a Martin guitar, a concertina, an accordion to accompany himself with.

Are you sure picking at the bones of folksong in this manner is productive. deriding others efforts.
'Mediator' sounds to much like 'medium' - communicating with the dead. When look! this thing is alive, it moves!!