I don't think the story is ever that Willow shouldn't try to learn to be a better witch or to find her own power. It's an empowerment story for Willow too. She has serious issues, and they get emphasized come season six, where she ends up sinking by far the lowest of any of the main cast. If you took just up to season six, there is something weird in the way you can read Willow's story as a repudiation of intellectually acquired, abstracted power vs. intuitive, essentialist power like Buffy has. But then, Willow is more powerful than Buffy, and saves the world, in "Chosen," doesn't she? I think discussions of Willow focus on the dark because it's so very well crafted the way the dark rises in poor lovable Willow. But Dark Willow and Chosen-era White Willow come as part of the same package. The way Joss is dealing with Willow in the always-popular season eight is with ambivalence--Willow states that she feels herself that she could go either way (good witch, bad witch). She's definitely empowered, in part by Buffy's entry into her life. But power isn't necessarily good or bad.

And the paradoxical thing is that going dark (I'm talking about Villains-Grave) is actually a very good thing for Willow's personal development--how else could she possibly release all those years of frustration? How else could she learn the strength she gets in season seven? That her strength comes at the cost of Rack, Warren's skin, the Magic Box and, most importantly, Tara (sniff!) is disturbing and scary and heartbreaking.