Have we considered the possibility that in terms of performance we are rather akin to actors, who think nothing of learning an accent or dialect for a role. Problem is, we don't keep it up for a seried of songs and spoil "the willing suspension of disbelief" and maybe that's what grates on the audience.

Two truths:
Once there was a man called James MIller who was born and raised in Manchester, England. He had Scots forbears, and when he took to singing, freely interchanged his working class Mancunian accent with a broad if unidentifiable Scottish dialect. Once he became Ewan MacColl, he then presumed to lecture the rest of us mere mortals about singing from your roots...

and

a quote from Dave Swarbrick, who when asked by Carthy if they could do something to a particular song replied, "Martin, the music doesn't mind.

Keep the faith

Chris.