So?
and the us has higher domestic birth rate than China
Nope.
US population would be going down without massive immigration. And China's population is actually going UP, with no immigration.
US population would not be going down without immigration, it would jus the growing about half the rate, which is still faster than China. And with working age, the comparison is even more in favor of the US. Plus Chinas behavior towards its own tech companies combined with Russia/Ukraine and Chinas rhetoric towards Taiwan has every large Us company looking to move production out of China. China is where Japan was in 1985.