At first I thought that by power-level you meant using the automatic Level 100 Character Boost feature they recently rolled out with.
It's hard for me to imagine anyone having a problem with the method that you described. By the time most of us are power-leveling our next characters, we've already had the new player phase, and we've already taken our time to explore how things actually work in the game. There are too many good reasons to power-level to get to max as soon as possible:
- You don't like the story, or you've done the hard part already
- This next class suits your playstyle better / you're just better at it than your previous one
- The first character was a trial phase and you want to really go the distance with your next one
- Your friends need you to fill a role at max level as soon as possible
But I totally get what you are saying about missing the story if you're power-leveling your first or main toon. But not everybody plays this game to take part in the story, or they just decide to leave that until a much later time. There's nothing inherently wrong with that either.
My opinion is that one should jump into WoW fresh, for the very first time. Explore everything, make mistakes, learn how professions work. Friends can wait -- if you don't like it from the very start, then it's just going to feel like a chore if you hit 100 tomorrow and you just do all the things people
tell you to do.
The most important thing (and I think almost everyone will agree) is to
learn your class. And that's something you won't get if you roll a fresh new class using the character boost option. I took both a warrior and a priest to level 100 from the beginning and I loved it. But I haven't the darndest clue how to play a rogue, and so the last thing I want to do is have a rogue at 100 and just wing it. That's when I think power-leveling is efficient, as it'll be both fun and beneficial to learning how to play it, plus I'm quite familiar with the lore and the lay of the land already.