for Dean I think it was the first step toward becoming a leader and not just a follower, the good little soldier taking orders

I think the transformation may have started in "Lucifer Rising" when Dean forces Castiel to make a choice. That whole exchange with Castiel struck me as Dean starting to make the turn toward leader as he needed to be someone Castiel would follow.

This episode, though, as you describe is the first shining example of Dean being a leader. Yeah, I like your ideas.

I do like your interpretation of Zach, too. I've been puzzling that one as well as I can't buy that Dean really is a vessel.