I'm assuming this is Ion1 because only full Ion is worth mentioning in this debate.
Didn't Anti-Monitor rely on his tech or other powers ups fairly often?
He started out with his towers to do dimension smashing, and wasn't *too* powerful when the heroes came to confront him in his fortress. Then came his attempt to smash the beginning of time, where he drained all the heroes and got *really* uber. Then after that was used up, he tried the anti-matter cannon, and tried draining two suns (which had been sabotaged to him).
Base-Anti-Monitor was powerful, but it's only when he was under all-heroes powerup do I think he could solo. Baseline AM I think either Parallax or Ion could take.