You are making a lot of sweeping generalisations there. No-one is denying that there are some songs that are ancient, or which appear to have originated outside any of the main commercial spheres; but the number of cases where there is actual evidence of this is very small, and that is the point that is at issue.

On what basis do you characterise the writers of broadsides as outsiders? They belonged to their times just as much as everyone else. I don't understand at all why you think they couldn't have written these songs, or at least the original texts from which the songs developed. Nor do I understand why you think a song must originate within the singing community in order to belong to that community. Nor why you think that 'realism' can only be achieved in this way. Surely it is just as plausible to suppose that of the thousands of new songs composed each year, a small number happened to possess the right attributes -- be that realism, singability, luck or whatever -- to ensure their survival within the singing community.

Also I think we need to be careful about drawing parallels with the singing tradition outside England. The existence or otherwise of a ballad tradition in Scotland (where Tiftie's Annie originates) doesn't allow us to make assumptions about what took place in Devon or Sussex.