Until the Patreon proves me otherwise, I'm backing Witch(-)/Seer(+). By my reckoning they're the "optimization" duality; a Seer pathfinds the best possible axis of their aspect (e.g. Seer of Mind = scans possibilities and identifies the ideal locations to make alterations to), and a Witch concentrates their aspect to spike in intensity around them (e.g. Witch of Space = main non-First-Guardian-related ability seems to be size manipulation).