There's still a short-term dependency ratio crisis brewing. Healthcare and eldercare are very labor-intensive, low-productivity industries; if you "prioritize" them such that all of the old get adequate care, the rest of the economy is going to be severely starved of workers. That's going to cause a standard of living drop that working-age Chinese may or may not be okay with.
Over the long run a lower population usually leads to higher quality of life for each individual, but you've got to get to the long run first.
