I don't believe that you discredit the curse by disproving the link between Demise and Ganondorf. The problem with this, is that we are getting into specifics, I believe the curse is much more general. He curses the those with the blood of the goddess and the spirit of the hero, this has nothing to do with the ambition for power, the triforce, or anything of the like. It's just that the hero and the reincarnation of the goddess will have to live a blood soaked life. Not a life of peace, but a life of war, and he succeeds at this curse. The key here is reincarnation. Zelda, and there are many different Zelda's all with different personalities and motives and are in general, just different people, all share the fact that they are all reincarnations of the goddess Hylia. It's just by tradition that the princess of Hyrule is called Zelda, though the name of this incarnation could be anything, i.e. Tetra. Just like the different incarnations, the different people that embody Hylia, the same can be said for Demise. You could argue that Vaati is an incarnation of Demise's hatred as well. He does not seek the triforce, he has different motives, different ambitions, however, succeeds in causing a life of war and battle for the Link and Zelda, thus fulfilling the curse. Ganondorf, though he is revived multiple times due to possessing the ToP, is only a incarnation, he's only PART of the curse, he is not, in and of himself, the curse. The curse isn't even specific to the goddesses or the land of Hyrule, it's only towards the reincarnations of the hero and the goddess Hylia, and game after game, they are the ones who face the struggle, no matter who the villian is. The curse itself, sets up the numerous adventures that Link and Zelda go on, and it explains why it is always these two that have to face it and not the other numerous Hylians, Gorons, and other races in Hyrule.