Exactly. Extolling the virtues of low population growth because it enables a higher quality of life is misguided. Your life is higher quality because billions in China are toiling away in inhuman conditions, making goods for you, and unable to move to your location.
Eventually they will indeed run out of people willing to do lower level jobs in the factories, then economic growth can move somewhere else. Bangladesh, Africa, Philippines perhaps?
Then we observe these countries whose population subset is actually able to move to a different, richer location (such as Maghreb countries) and we see apparent lack of serious economic growth, industry development and general instability.
Makes one question all of your assumptions.
Before you yell at me consider that China lifted an unprecedented amount of people out of even more inhumane conditions as a result of this process.