I agree that WoW is a waste when considered in relation to the space of possible things a young person can be doing. In practice, though, teenagers are basically trapped in their school related social circle and activities. For me, WoW was a place to
be someone else, other than who I was at school, and to feel valued for reasons beyond my performance in high school social games.
Beyond that, I legitimately think that my experiences with raiding, min-maxing, grinding, etc. were a sort of preparation for the social dynamics of... corporate leadership. Of course, a lot more was required (technical skills, philosophical grounding, etc), but it was a good start.