That's a fair criticism, I did force it into that meter. You are right that sound-wise 6/8 and 3/4 are identical but preserving the 6/8 form helps the beat line up consistently in your mind while singing, whereas 3/4 makes it in the middle of a counted beat.

A minor nit-picking, but 12/8 is functionally similar to 6/8 except because it's longer the points of emphasis change slightly. The end result is that the 7th beat (in my example, the "A" of "A-a-WAY") is not emphasized as much in 12/8 since time signatures emphasize the start of the measure over the middle. However, it's a very minor difference, like I said.

I am inclined to agree that it started life in 6/8 and was slowly corrupted by a combination of people who were less musically-inclined and the folk process over time. Once they found a version that worked for them, they could just stick with it.