10 million people are sufficient if those people are reproducing. If they aren't, the population keeps shrinking. Maintaining their genetic diversity ends up not mattering much. For an imperfect analogy, contraceptive methods, including abortion, are to humans what antibiotics are to bacteria: populations "vulnerable to" condoms and the like lose in the natural selection competition, while those that "mutated" and gained "immunity to" condoms etc., by continuing to grow, replace them, becoming over time the majority, then almost totality, then totality, of the population.
As for your example involving numbers, that's incorrect. $2.88 million sounds like a lot, but if you look at, say, Botswana, $2.88 million of their currency buys almost nothing. Why? Because the concrete meaning of $2.88 million is "All_Stuff_in_the_Market times the number 2.88M divided by Total_Number". If All_Stuff shrinks, or Total_Number increases, or both, that 2.88M can buy less, and less. Or to put it another way, society experiences inflation. Any scheme you find to grow that number faster than the number others hold means that you get a higher percentage of All_Stuff, while those others experience a lower percentage.
Greater production can fix this, yes, but only if the growth rate of All_Stuff is consistently faster than that of Total_Number and is relatively well spread among the population (it won't help if a tiny slice of the population grabs most of All_Stuff). Can better technology cause that? Maaaaybe. That's the bet the optimists make. There's no guarantee it will. Right now, the only thing we know that, with absolute certainty, causes All_Stuff to grow faster than Total_Number, is population growth.
Hence, the elites of most countries facing this issue are opting for increased immigration. If the population started reproducing faster, immigration wouldn't be needed. Since they aren't, immigrants it is, at the pace necessary to keep All_Stuff growing faster than Total_Number, which is to say, under acceleration.
The other alternative is the population learning to live with less, and less, offset a little thanks to advancements in technologies, but by no means completely. That is to say, the population accepting their progressive third-world-ization.