To clarify...
Superman and Ultraman were dualities: comprised of normal matter/good, and anti-matter/bad.
Thought-Robot could only be activated by the tremendous energies unleashed during collisions of fundamental opposing qualities:
https://i.imgur.com/FsHrHjh.jpg
So Allen merged the essences of Superman and Ultraman(ie. matter and anti-matter), and used the resulting energy to activate Thought-Robot:
https://i.imgur.com/5LRkLT9.jpg
https://i.imgur.com/L3YM0c3.jpg
But make no mistake: once activated, Thought-Robot was exclusively channeling the the idea/story/concept of SUPERMAN(ie. the most powerful story in DC.) Hence Allen's final line: "Only Superman can save us now."