I'd argue the White Witch's magic is fundamentally uncreative. She can't make a living thing. She can only twist, freeze, or mimic life (like turning the party to stone in mid-celebration). Aslan creates life—he breathes life into the stone statues, he brings spring. He sings Narnia into existence in 'The Magician's Nephew'. Creation is the ultimate magic, and it's entirely outside her domain. She's a parasite on creation, not a creator.
You know, the breakfast scene after the resurrection says a lot. Aslan, this immense lion, is romping and playing with the girls like a giant kitten. That contrast is vital. He's not just a war leader or a distant god. He's joyful, affectionate, and alive. The Witch is all cold calculation and sterile pride. The battle is, at its root, a contest between joy and misery, between abundance and scarcity, between life that celebrates and death that hoards. Aslan's playful, generous nature is as much a weapon against her as his claws. He's central because he offers an alternative way of being that is infinitely more attractive than her bleak rule.