adding over 7 million people is what's important

It is not. When dealing with statistics, percentages are the only thing that matter.

If it was a country like Canada, with a population of less than 50 million people, that would be problematic.

Losing 15% of your population on a yearly basis isn't problematic, it's species-ending catastrophic.

But with a population pool of 1.5 billion, what's the actual concern? What social instability does this cause that a population of 1.5 billion already doesn't?

To put it in perspective, that's the same population loss ratio that japan is currently experiencing. Japan, the country that's teetering on the brink of cultural and societal collapse from an aging population.

There will never be too few people in China

Yeah this sums up the problem fairly well. You're so stuck in your personal opinion of china's population that you can't imagine for a moment the situation changing, regardless of what the data might be saying. You're no better than the people who refused to believe climate change was occurring. Fuck your gut instinct, pay attention to the actual numbers.