The ring is useful when attacking with obviously weaker troops, but it might be less useful when dealing with larger groups of creatures and fighting against a powerful Father Dragon.
Well, I understand your position, and I doubt I can convince you otherwise :), but why aren't you taking into account (with the example of the "Father Dragon's power") Armageddon? Does immunity to Armageddon for your troops mean nothing to you?
And regarding the ring, I suggested comparing it not to the power of the Father Dragon, but to the Cursed Armor...