if the DC universe is as large as ours, shouldn’t the number of Green Lanterns be in the millions if not billions?
Well, maybe the universe isn’t as densely populated as you think. It may be reasonable to assume that each sector is about as populous as our own.
What HCQ said, but another point: As near as we can tell, our universe is also not a sphere, while the DCU pretty explicitly is. So, if it’s a different shape from our universe, it might as well be a different size. That could be either tied to or a cause of all the wonky physics in superhero stories, too.
They been around for 2.9 billion years
They need more!