I don't see Willow as a pure scholarly type. She doesn't obtain knowledge just to become more knowledgeable, you know, as a goal in itself, but also to become more powerful. Basically, Willow views knowledge as a source of power. Her approach to magic reflects that - it's nowhere near academic, it's a self-taught DIY freejazz graffiti punk hacker type of deal. Even in season 10, being the seed's mom and having all that incredible knowledge she's still all man, #@$& Latin! and might even cast a spell with an incantation like Boom Shaka Laka! and I mean, really Will, really? 'Cause there's nothing to gain from learning Latin, so #@$& it, right?
So yeah, Fred's smarter. She's the genius prodigy professional researcher type, Willow, on the other hand is a freaking mad scientist slash MacGyver who nonetheless gets shit done.