^ TOAA is only omnipotent within a balanced and well-functioning system. If that balance is upset/unhinged, however, then TOAA's omnipotence can become less than absolute(as we saw when Thanos absorbed the regulators and such)... But that's neither here nor there.
As for GEB: it doesn't seem to have any sort of personal "vendetta" against the DC continuum, to the point where it is choosing to launch an all-out assault on the omniverse -- but rather, its power is being used/harnessed/manipulated by Pariah(and co.) as a means to an end. Probably best to wait until the story has wrapped up to make any concrete conclusions, but based on some of the feats GEB-amped characters have preformed(in addition to some of the statements made about GEB itself), the heavy implication is that it is one of the most powerful forces that has ever existed in DC.