Gunn and Safran are putting the DC universe on film the right way for the first time. Those characters all live in that world and it would be weird for the film to pretend they don’t. We’ve done so many movies with a single hero as the center of the universe, it’s time to do comic movies right.
Yes, humanity was very close to extinction and sub 10,000 in population at one point. We can tell from mitochondrial DNA.