It is hard to disagree with Mormon that this destruction of Ammonihah is a fulfillment of the prophecy of Alma (as mouthpiece for the Lord) against them. Mormon, however, wants to press home the complete victory of the Lord over Ammonihah. In Mormon's narration, the story of Alma and Amulek in Ammonihah is a symbolic confrontation between the two great ideologies that we see in the Book of Mormon, the Nephite religion and that which has been labeled as the order of the Nehors, even though we may clearly trace its roots further back in history than the man named Nehor.
In this symbolic confrontation, we have the Lord against those who would rebel against the Lord. The predicted destruction not only comes, but comes with a vengeance. Ammonihah is not simply destroyed, it is utterly destroyed. It is not simply humbled, it is humiliated. It is not simply uninhabited, it is uninhabitable. The description Mormon gives is more than accurate, it is his structural contrast to the pretended greatness of this city, which withered before the power of the true God. As in the Old Testament, the fact that a mortal enemy was the means by which the wrath of God was carried out does not change the essential facts in the least. For Mormon, it was God's vengeance that was wrecked upon Ammonihah, in accordance with the prophecy.