I think the PPP calculations may suffer from the same problem as the USA inflation rate being nominally low. Housing, food and medicine are all ludicrously cheap outside of tier 1 cities.
You might want to compare Singapore with a city like NYC or London, not with a territorial state. It's pretty normal around the world for cities to be replenished mainly by people moving in.
(Of course, to be fair you then also need to compare GDP per capita against other cities. And they usually do a lot better than territorial countries that include a lot of hinterland.)
> A low TFR is indisputably the slow death of a society.
No this is a non-sequitur.
Low fertility only means that the affected society grows smaller. This is only equivalent to "slow death" when it persists for centuries until the society is actually dead.
Whereas a society replaced by its own children maintains continuity of community, nation, or broad grouping of people having common traditions, institutions, and collective activities and interests
PR China is still pretty poor (around 31k$ gdp per capita adjusted for purchasing power) and its growth has lost a bit of steam recently.
You should wish your country to be more like Taiwan or South Korea. Or Singapore.