I think the term "source singer" is a very useful and accurate term.

Perhaps you would accept that it is a term that only has any use if it IS accurately applied and also that so often it is not accurately applied.

A claim like: Her grandmother, for example, was the source singer for the well-known song Bunch Of Thyme which is now widely sung.

It is only the start of many pointless arguments and counter claims - none of which have much to do with the song or the music itself.

Studying and labelling of the music may be judged to be very important (mainly to those who do it). But it will never be as important as the music itself.