Rather paradoxically I am quite suspicious of academic assertions from earlier periods. They often had deadlines to meet and pressure from above as well as internal politics. There are as you might expect some exceptions to this like David C Fowler who openly make their assertions backed up by plenty of examples and evidence. I am not an academic and came to my conclusions re Peter Buchan by looking closely at the actual ballads themselves, before reading widely round the subject. It was only after this I came back and looked minutely through Child's extremely disparaging comments in his headnotes.

You only have to look back at the ridiculous assertions of the likes of Kittredge and Gummere, both Child's pupils, re communal creation, later thrown out by another pupil, Louise Pound, and others. More recently David Buchan's use of Anna Gordon's ballads to present his discredited theory that her ballads demonstrate the presence of oral formulaic theory in 18thc Scotland. It is easy to see now that this is ridiculous when we can study all of her versions side by side in Emily Lyle's excellent book.