'far from merely 'telling a story' they involve complex muli-layered plots'. Can you please give us an example, Guest, guest? I must be missing something. The only complex, multi-layered plots I can think of are those that have been concocted by the antiquarians. The vast majority you can write the plot out on the back of a box of matches.

'The great classic ballads have structures which suggest a sense of 'school' of writing/composition.' This interests me. I too feel this. In fact I go along with the school of thought that thinks a large number of the 'classic' ballads were put together by antiquarians and collectors of the 18th-early 19th centuries.

'Lord Randal' and the 'Maid Freed from the Gallows'. Whilst I agree with the lack of explicit plot here there is plenty of implicit plot.
Child largely included them for their ballad-like formulae and their relationship to other fuller European versions. The Maid Freed is also found in cantefable form where it is only a small part of a really complex supernatural plot.