I like your thinking on this, would be a good way to explain in game the truth about the nature of the powers. Because the misconception one that was deliberately made to fabricate the final plot twist and Mara would be best suited to figure it out and reveal it to everyone. Aside from some Deus Ex monologue. And with the Witness in there, gaining control over Light allows him control over the physical, ie damage Strand and Veil containment lore has been about revealing the two powers are twinned, not separate. Think about how Bungie labeled them, Creation and Consciousness. Or what Osiris said about how the Witness was able to hijack our Ghosts. Creation makes the body, Consciousness the mind. Those work together, not separately. So Prismatic isn’t a new power, it’s how the two are meant to be. And a showcase as to why they were separated, cause combined you have theoretical control over reality. In game, NPCs have only seen them separate and at disparate ends. Let’s look at your example with Mara. She remade their minds and bodies. Dark and Light. So the Creator of the universe also HAD to use them both. That’s what all this is building up to. It’s not a major revelation to us because the concept has been around since base D1 when the Fallen called Guardians “the darkness”. We’ve known this was a potential outcome and it makes the final twist that much more flat. Really the big reveal is going to be the Gardener and her schtick.