I think, bottom line, the YED doesn't understand love and sacrifice at all, and has mistakenly discounted its power.

Oh, I'm absolutely convinced that's one of the themes they're playing with here. Like Buffy, Sam's surviving/evading being turned evil by YED because he's got a support system in place (Dean's a little better than a scared guy with a rock, after all), and it's driving YED crazy.

What I liked about the Meg element is that we finally got an inkling that there are various agendas at play in the demon world, and not all of them are consistent. Meg, or whatever the demon's name is, may end up interfering with YED, even though she's YED's child.