"Doggerel" is, by definition, trite or clumsy or otherwise faulty. A traditional song shouldn't have these attributes, but the best ones tend to use short, Anglo-Saxon words rather than longer Latin-derived ones. If you want an example, look at the Border Widow's Lament in the DT (not the one with 2 after the title). There's only one long word (extremity) - all the rest of the vocabulary is as a simple woman would speak, which makes it very direct and touching.

Another point: if it's written to fit a regular tune, the lines need to scan rather than being sqeezed into the metre. Nothing marks out a fledgling song more than a badly-scanning line with too many syllables or the stresses on all the wrong places.

Marje