This universe was generally on the weaker side. Not only was Superman relatively weak, Brainiac was too. The fact that he could ultimately be physically destroyed showed that, compared to a super artificial intelligence, he was more like a super robot—not that difficult to deal with.
However, Bruce and the others had not planned to deal with him. They merely had Barry travel through time and bring back Lois from before Joker killed her, then had Superman resolve the issues between the two of them while Batman took the troublesome Wonder Woman away. That would solve most of this universe's problems.
Then Bruce returned to his own universe—he needed to negotiate with Brainiac.
After that run where he had come extremely close to success, Brainiac gave it another try and succeeded, just as expected. Although their universe was still in 1999, more than three years had actually passed.
Considering that the invaders had all been major figures in the universe, this was already an excellent record. As a super artificial intelligence, Brainiac supposedly had no emotion called "tired," but once everything was over, he still felt excessively worn down.
At present, Brainiac had completely integrated all the resources in the Solar System. Whether it was Earth, Mars, or Krypton, every living being and every resource on them had been allocated to the utmost extent. Even the gas giants had been put to use, and the entire Solar System was operating at high speed.
Under immense pressure, humanity on Earth could forget about any Human Federation. They had gone straight to rationing. The final stage of socialism had been achieved in one step; private ownership no longer existed. Everything belonged to Brainiac, and everything served the war.
Humanity had become unprecedentedly united, though of course that had not been their choice.