Well, well, I am surprised! And yet it's hard to deny the truth of some of that; the character development and exploration is certainly there, but it's also subsumed to a large extent by the demands of the Shounen Retard manga (fight, fight, fight!).
No Kyo/Yuya is unthinkable for SDK. People are free to dislike her if they want (though does anyone actually dislike her? She's fundamentally likeable, I would have said), but most of the story wouldn't be happening without her.