If the anti-spiral himself fights Lelouch, it's not going to be in the galaxy sized mach. He used that to match TTGL. Both the anti-spiral himself and Lordgenome establish that when the Anti-Spiral himself does battle, he matches the opponent to fight on an equal playing field. Furthermore, unlike giant robots, the anti-spiral won't have had tremendous amounts of experience using abilities like those Lelouch possesses.
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Dying breath, light my blade and sing in shadow! Omega!