I think it is the way it is collected and distributed is the problem, Pound for pound the PRS money paid by the venues and concerts i attend are not proportionally distributed to the peoples who's music i am listening to, if only 5% (arbitary hypothetical figure)of the income of PRS goes to the folk industry they should only pay 5% of the fee. A fairer way would be to charge per song and distribute accordingly, at first it would seem to be an administritive nightmare but on line tax returns seem to work so why not on-line PRS returns.
I don't write songs but I do significantly "tweak" them,occasionally I do hear my tweaks being repeated by others but I don't expect to get paid for it. The one to ask would be John Connoly the writer of that fine old traditional song Fiddlers Green, it's personal info, but you once saw a version of it on most juke boxes, I wonder if he got his fair share of the PRS pot.