If the attributes are identical with the simple divine essence, then they have to be identical with one another; otherwise, we will end up asserting that the attributes are parts that compose God, rather than being identical with God's essence and with each other.
You make a couple of important points here, Daniel. I appreciate the language Duby used to explain this when he speaks of the attributes of God as referentially identical, but denotatively diverse. That's the neatest encapsulation I've encountered so far. Indeed, the language of "attribute" should be taken seriously, because the element of human perception seems baked into the crust in a way that would not be true of other terms that could be used like "quality" or "property." Ectypal theology attributes these attributes to God because what is one in the archetype is considered under various aspects according to the limitations of human understanding, which cannot comprehend God, but partially apprehends "the outskirts of his ways" (Job 26:14).