".The problem with definitions is that the goal posts move too regularly."
Not a problem if you remember you're talking about a specific music and not football
Folk song has nothing to do with tase or "prettiness" - it's a song which has evolved in certain circumstances and has passed thought a "process" i order to have become folk
Whatever people choose to call fork, it if hasn't undergone that process, it ain't folk - not a value judgement, just a fact

What you describe with your Traveller depends on what happens to the songs he made and the state of the Tradition when he made them - if the tradition is in good shape and his mates took his nongs up and made them their own yo have a folk song - if niot, they're just songs made by a Traveller and any song that anybody made could be described as folk

Music hall songs tend not to change and adapt - they remain as written and the fact that they are/were usually copyrighted, they remain the property of the composer - not the folk

The language only works if those using it agree on what the words mean - if they don't, we stop talking to each other and - in the case of folk, all the clubs stop functioning because nobody can agree what they can expect when they turn up to one

It is misleading to say the old singers didn't differentiate (certainly when you are talking about living or not long dead traditions)
The singers may have sung every type of song but that didn't mean they couldn't tell the difference between the songs Harry Cox sand and those sung by Harry Champion

We seem to have reached the situation now where 'Nellie Dean' is a folk song and long ballads are "inappropriate" - or so I've lately been informed
Folk song comes with a lot mor baggage than "just repetition" - if it didn't, we'd better send all our books to Oxfam
Jim