Agreed!!! It might also be useful to establish an agreed definition of "purist" so that we might be able to discuss and then perhaps, answer, the original question which forms the thread's title.
As we cannot even agree a definition of "folk music" it seems unlikely that we can agree what constitutes a pure interpretation of it.

I might add that my calendar tells me that I have present at around 75 live folk music events this year so far. A few of them have been disappointing but they are outnumbered by those that I have left feeling uplifted by performances of traditional song and music by performers from England, Scotland, Ireland, France, Wales, The USA and Canada. These included quite a number by younger performers that I had not seen before and I would like to name Daoirí Farrell and Cohen Braithwaite-Kilcoyne amongst these.