Not every Batman kept his mouth shut. Or rather, Batman only kept quiet about the less important matters. A catastrophic invasion concerning the survival of the Multiverse was obviously not one of them. Most Batmen would discuss their battle plans with the Justice League. Of course, perhaps those who seemed cheerful simply had no other options.
Ideally, Batman would devise a perfect plan and tell everyone what to do. But in practice, that would not work, because if he did not explain the plan to the others, they could not carry it out properly. Worse, if they were not involved in the planning process, unexpected problems would arise during execution.
This had nothing to do with democratic procedures. It was more like a top student explaining a problem to a struggling student. Throwing out the answer and expecting them to reverse-engineer the process would never work. He had to guide them through it step by step, letting them calculate the answer themselves. That was the proper way to teach.
It seemed like a waste of time, but that preparation now proved useful. The other members of the Justice League had all heard, more or less, about Batman's plans. Some had built incredibly detailed surveillance systems to prevent anyone from suddenly coming back to life; some had opened passages leading to the Earth's core, ready to awaken the Spirit of Existence at any moment; others had delved deeper into magic and the seven Lantern powers, believing that only a stronger mysterious force could defeat the Black Death Emperor.
Most Supermen favored the last option. Passive defense was no solution. They could not let the Black Death Emperor pick them off one by one like a sniper. Even if they won that way, the Multiverse would be left riddled with holes. It