Hmmm.

Well, for one thing, I actually don't think that such internal evidence as there is supports your conclusion. At the very least the picture is much more complex than you make out.

If the songs sung in rural communites were made within those communities, why do they only rarely contain information that would be limited to those communities, such as detail about farming practices of the time? Why do so many of them present rural life as a pastoral idyll, rather than a never-ending cycle of backbreaking hard labour? Inasmuch as it's possible to extrapolate from the lyrical content of rural songs, an origin in the pleasure gardens actually seems more plausible for most of them than the idea that they were written to reflect the realities of life in rural communities. Because, as far as I know, many of them don't.

As far as I'm aware relatively little is known about the lives of most broadside writers. It's a massive presumption to assume that they were 'desk-bound urban outsiders'. I'm not even convinced that that is a category that can meaningfully be applied to anyone in the 19th Century. Was Dickens a 'desk-bound urban outsider'? Or Conrad?

No doubt there are some similarities between the English tradition and the Scots and Irish traditions, but there are also obvious differences. And again, I don't know that all the evidence supports your ideas. The ballad tradition in Scotland and Ireland is both oral and literary. Some well-known Scots ballads are of obscure origin, others were composed by well-known literary figures, some are disputed.