@GY: I'd argue she plays small roles.(and frankly, everybody knows how awesome Impa is in SS, and that she's cool in OOT). What we don't know is how awesome she is everywhere ELSE.
Zelda's key to all the games(except a very select few. Majora's Mask, Phantom Hourglass, Link's Awakening), Sheik is a major part of Zelda as is. Likewise, Sheik is much easier to make a moveset for, as Sakurai didn't need to use Link's abilities for her. That's proof alone. Zelda wasn't given her own unique moveset using her own powers. In fact, the only one she has is the Light Arrows. But that's it.
Anyway, yeah, this is ridiculous.