Strictly speaking, Zurr-En-Arrh had originally been a Batman who existed in some reality.
On Planet Zur-En-Arrh, a certain element within the planet enhanced the bodies of Earthlings, allowing them to rapidly gain Superman-like powers, much as Kryptonians did when they came to Earth.
Bruce Wayne had once visited Planet Zur-En-Arrh and spent some time there as a Superman.
That experience had prompted First Batman to reassess the relationship between Metahumans and humans. He had stopped being so hostile toward Superman and truly become part of the Justice League.
Interestingly, however, when Bruce once found the time to build a Spatial Jump Device and entered the coordinates of Planet Zur-En-Arrh, which he had visited before, he discovered that no planet existed there.
There was not even a star system there, only an endless expanse of space.
Bruce had personally recorded those coordinates. They could not be wrong. The only other possibility was that the experience itself had been false.
Bruce quietly stopped mentioning the matter. But to commemorate his time as a Superman and the Alien Batman who had stood alongside him on that planet, he created a Zur-En-Arrh Personality within his own mind.
Thus, when the Zur-En-Arrh Personality bypassed Bruce's defenses, responded to a suggestion, and actively interfered with First Batman's subconscious, Batman's thinking gradually began to change.
He began seeking Brad out for frequent conversations and learned from him part of the truth about how serious the "shrinking" was.
DC would soon perish.
Brad was an outsider to DC, just as Bruce Wayne had been an outsider to that mysterious Zurr-En-Arrh back then.
Bruce had helped Zurr-En-Arrh weather a crisis.
Brad might not be entirely bad for DC.
The change occurred deep within his subconscious, seeping in silently. Nor was it an intrusion from outside, such as psychological hypnosis.