I think that's my whole gripe with the "Lost Soul/Mirror" thing; The Lost Soul's in-game profile says that those who encounter it will have no chance to change their fate and will instead be inadvertantly led towards it, or something along those lines. But isn't that the whole point of the word "fate?" Isn't that exactly what fate is, an inevitable outcome? You can't change your fate regardless of your actions, your destiny is your destiny, with or without a magical device (or in this case, "The Lost Soul")telling you so.
That's what my whole point was. Despite the "character" of the Lost Soul, the Belmonts are still destined to battle Dracula no matter what, and everything that happened in MoF still would've happened without "the manifestation of the mirror" being there. But now I'm starting to confuse myself. I'll just chalk it up to awkward storytelling on MS' part.
Concerning Zobek/Lost Soul connection:
I personally don't think they are one in the same. Although they do have similar voices, do remember that the Necromancer says that Zobek sent him to retrieve the Combat Cross to deliver to him. Why then, if Zobek is indeed the Lost Soul, would he willingly lead Simon to it? That doesn't make any sense.