I agree with you Finky baby.
Jook, I remember reading in the dreaded Awake magazine back in the early 80's that it was thought that approximately one third of people who had ever lived were alive at the present. This typical Awake factoid fed into the idea that a resurrection would not overburden the Earth.
Recent more researched statistics as I understand, puts the total number of Homo sapiens lives ever lived at around 105 billion i.e. about twelve or thirteen times times the present population.
As you say, who can really know but this was a serious statistical attempt.
The more bizarre aspect is to talk blandly about a resurrection of billions of people when not one person ever in all of human history has literally been resurrected.
Let alone having a refugee crisis of astronomical proportions...
Waring a sane non-religious hat...To imagine billions coming back to life is absolutely and unconditionally preposterous!