Gotta love people who dont pay attention to the story and then bitch about it. He had a plan, it was to take over the Forge of Origination and reshape Azeroth into Ny'alotha. Then we used the Forge on him. It was not some "pewpew lazor beam". It completely originates it's target. You can't really have a defense against something that removes you from existence.
Then once we got into Ny'alotha. His backup plan was to let us get to him and use our Heart to direct link into the Heart Chamber to take Azeroth from there.