There is one problem with the current US system: it overproduces talent. When the US system was growing rapidly, the people could build a long-term career in the US. But nothing can grow forever at an exponential pace. The US continues to pour plenty of money into STEM, but it can't keep up with the pace of grad student production.
People are making smart, individual decisions to head overseas for work. Places like China are rewarding them.
Wait what? I know that many Chinese students are staying in China, but this is the first I've heard of a substantial demographic immigrating to China to work there, esp from the US. Do you have data?
I am European and I do basic research in science. They seem to be very interested in fundamental science and investing heavily in lots of subfields. As discussed in other comments, the improvement in their research quality during the last decade is nothing short of impressive.
Plus, from this one can infer they are clearly scouting researchers in a systematic way.