[bzbarsky]

> China had a literal one child policy

The operative word being "had". It hasn't had one in a while.

> Population grows exponentially

It really depends. It does if you assume TFR is a constant, but it tends to not be constant.

> I don’t think we should look at it in decades but rather as through lenses that capture time in centuries.

In the "centuries" timeframe, technological change (much reduced infant mortality, availability of contraception, career opportunities, etc) pretty much dominates the TFR situation.