"I just think that the best traditional singers assimilate material to their own style"
Ewan always made the point that he wasn't a traditional singer and his songs were't folk songs
I know he picked up songs from both parents (I was told by someone who knew both in the early days) but I don't think there were many that he didn't fill in and adapt from books
Who doesn't do that ?
I'm from Liverpool and had (and sometimes have) a broadish Scouse accent what do I do - I wouldn't sing most in a Liverpool accent - ballads would probably sound ridiculous   
I sing quite a few Irish songs but would rather have my fingernails torn out than try an 'Oirish accent'
What do I do ?
Many singers I knew way back were teachers who needed to loose most of their own accents to hold down their jobs - do they sing everything in Standard English ?
We all adapt to the song to some degree ot another
With Ewan, this wasn't a reviival thing - it was happening far earlier