China has a better gender balance than India and they have 5x the GDP. The males will just get Vietnamese or Laotian brides.
China's fertility was already on the decline before one-child policy. Also contrary to popular belief, only about 35% of the population was subject to the original restriction. For instance, rural parents were allowed to have a second child if the first was a daughter and there were numerous exceptions over time.
Btw, the basis for the one child policy was because of a Western think tank called the Club of Rome that managed to convince key Chinese intellectuals that China's ideal population should be much lower because neo-Maluthusian ideology was trending at the time.
But a lower population rate likely was a boon for economic development during their rise, for instance because of less mouths to feed, less resources to consume, more resources devoted to a child. Check out the paper "Do High Birth Rates Hamper Economic Growth?" (Review of Economics & Statistics, MIT Press, 2007)
The research, spanning two decades from 1978 to 1998 and covering 28 Chinese provinces, found that the lower the birth rate, the faster the economic growth. The annual growth rate of the real per capital income during this period was as high as 8.1 percent. At the same time, the birth rate was very low—at only 2 percent.
Lower fertility leads to a higher level of schooling per child.
Lower fertility increases parental labor supply.
Lower fertility may facilitate parental migration, thus enabling the reallocation of the labor force from rural to urban areas.