>>>>If they are the same song (the texts suggest they are), is it not possible that a hack took a popular traditional idea<<<<

There are many examples of popular traditional ideas being turned into ballads. In fact this is what most of them are.


or was it originally a shorter song turned it into a self-indulgent epic?<<<<

The evidence points to the contrary when we look closely at the evolution of individual ballads over several centuries. However, the lengthening was very much an indulgence of the ballad editors like Percy, Scott, Buchan, etc.


Example of long into short. Marrowbones common on broadsides early 19thc becomes much shorter Music Hall song 'Johnny Sands'