I don't think the unknown God will be the final fight

Ok so this might be crazy but I think it'll be your sibling. Because you have multiple friends in the Fatui. But none in the abyss order. In fact you fight against them more then the Fatui it seems. So hear me out one of the first big fights is against the unknown God until you hear her reasoning and it's actually makes since. But the abyss attacks and you fight them trying to get the plan in motion. You team up with all your old friends until the final fight. You get separated form your group and have to face your sibling in one final fight.