Hello oetb. Before I comment on your question, I would like to make a couple of suggestions.
1. It is a good idea to quote the source of what you are quoting, if possible.
2. Also, when you quote someone at the forum (this is regarding your other comment that I just saw on another thread), please say who (at that thread) said that, if there are several people who had commented.
Now, regarding your analysis, Let me clarify a few things first.
I had discussed the sutta in question, Nakhasikha Sutta (SN 20.2), in the post, “How the Buddha Described the Chance of Rebirth in the Human Realm”
To quote from that post: “In the same way, bhikkhus, sentient beings reborn as humans are few as this bit of sand on my fingernail. But those not reborn as humans are many as the sand on this great Earth. Therefore, you should strive diligently and without delay to end this suffering in the rebirth process”.
I have highlighted the fact that the Buddha said that, “of all living beings” that die the fraction born as a human would be similar to the fraction of grains of sand that can be picked up on a fingernail to that on the Earth.
I just Googled and found that an estimate for the grains of sand on Earth to be about 10^19.
There are roughly 10 billion (10^10) people on Earth.
However, we need to take the number of all beings on Earth.
The article, “The Largest Study of Life Forms Ever Has Estimated That Earth Is Home to 1 TRILLION Species”
says there are over a trillion (10^12) species of living species on Earth.
– One of those species is ants. I did a Google search on just how many ants in this world and saw that an estimate was 10^15.
– That is just one species out of over a trillion species.
– Of course, there are fewer animals of larger species.
– But the number of microscopic living beings could be staggering.
– Here is a video on how many in a drop water contaminated water:
“How many living things are in a drop of dirty water?”
Of course, what I discussed above includes just animal species on Earth.
There are 31 realms based on the Earth too. We simply do not know how many living-beings are in the other three realms of the papaya, or in the Deva/Brahma realms.
It would be impossible for us to do such a calculation to get a meaningful number. But as always, the Buddha would know for sure. I personally don’t have any reason to doubt it.
The Buddha said there are four things that we should not waste our time on.
– They are: knowledge of a Buddha, jhana, working (finer details) of kamma, and details about the world.
See, “Acinteyya Sutta (AN 4.77)”
– a couple of English translations are available there.
I am not discouraging looking into things with an open mind. But sometimes, we are not capable of finding answers to some questions. In particular, the Buddha advised against looking into those four.