Ealon is a scam, he seems to be just another technocrat but way smarther than Swaps and his cronies.
There is no "right number of people" he is just priming us to think that someone should regulat such things, the same argument that malthusians have but the other way around.
The miracle of free market as a system to coordinate resources is that it will adjust to whatever situation we face, resources will be economized when and where needed, nobody needs to micro-manage how much people lives whether for shrinking that number or to push it upwards.
Something that is usually misinterpreted is the retirement system that is actually a ponzi that needs more and more people entering the pyramid scheme to delai its collapse, that is not an issue of having a low number of people, but an issue of the system itself that is basically an intergenerational scam