Walter was not a bad unaccompanied singer we are not talking about style. I am talking about technique, drifting a tone over the course of a 5 minute song. it is not the same as suddenly changing key during a song, he certainly would not be the first or the last unaccompanied singer to do so Walter sang clearly his diction was good and he held the tune. To describe someone as an embarrassingly bad singer ref;ects and tells us more about the critics lack of understanding of this genre of singing Stanron mentioned that he always sings with an instrumentto avoid this drift, however singing with an instrument may have that advantage but it has other disadavantages, it requires considerable skill to avoid forcing the vocals to follow the instrument, unaccompanied singing allows a much freer style of rythym, which can on occasions be desirable.
I have witnessed a revival singer singing with a guitar and singing a quarter of a tone out with her guitar that in my opinion is far worse. here is peter bellamy singing the same song with concertina, the song does not drift in pitch, but even with a concertina a rythym is imposed.
https://www.youtube.com/watch?v=C-ripmGRt8Q