Without making the performance into a melodrama, it should still be possible to convey the tension in a repetitious song like 'Hangman, stay your hand' or 'Lucy Wan' -- if the singer believes in it!

I agree, actually. I think my point was that we've got used to a different kind of song: one that doesn't (usually) tell a complete story, doesn't (usually) include a lot of repetition, but just moves along nicely for a couple of verses and choruses & then stops. In terms of interpretation, a song like that basically sings itself - it tells the singer what to do. Both the long songs and the repetitious songs give the singer much more work to do, & both can be a turn-off for the audience - if they're not done well.