I agree, but is this the right comparison? Isn't this framing obscuring the fact that in the trillion-people world, you are much less likely to be born in the first place, in some sense?

Rawls's veil of ignorance + self-sampling assumption = average utilitarianism, Rawls's veil of ignorance + self-indication assumption = total utilitarianism (so to speak)? I had already kind-of noticed that, but hadn't given much thought to it.