" If they can't or won't agree, how can you expect musicians to agree?"
They can't agree on detail - part of research of an subject.
Nothing to do with definition, which remains as it was until it is replaced.
Any replacement, if it it to be comprehensible and workable needs to be backed up with researched information - you have that with '54.
I've just re-visited the Funk and Wagnall Dictionary of folklore with the intention of putting it up here.
There are seventeen, double columned pages of it, covering many aspects of the genre including how song relate to other aspects of folklore and how English-language songs compare to those of other cultures.
Nowhere does it contradict the basic premises set out in the '54 definition, which is quite interesting in itself as it was published in 1949.
What you are talking about when you refer to other definitions (which you still haven't provided) is the misuse of the term, not a re-definition.
You have referred, quite interestingly, to physics - you dont stop the-man-in-the-street for information on the subject - why should you do so for folk song?
Jim Carroll