I think it is a bit overcomplicated / subjectively analysed.
The emigrant learners in the USA has to have money to finance the school from they own/parents pocket, and they consider the USA schools as good investment ,regards of later wage and immigration prospect.
After graduation , due to the high investment they want the highest paying jobs - and that happens to be in the USA again.
To change it China needs to improve the income opportunity for the Chinese university graduated persons, including but not limited the non monetary compensation , like long term stability and freedom enjoyed by the USA citizens/permanent residents.
Lot of student and family consider the USA university as an expensive, but sure path for emigration .
Money helps but for people with ambitions, a place where they can apply their advanced knowledge and have job satisfaction is just as important. Objectively, In 2021, America is still ahead by a long shot. America is still land of opportunity if you have the drive and the smarts. The quality of life is also superior and less stifling and once a person is settled down with family and kids and social circle, it is very hard to move even if there is potential for marginally better life elsewhere. Thus to expect the already established talents to make huge life style changes is unrealistic. If they stayed in research or academia, chances are money is not their primary motivator. Of course, if the U.S. suffers a prolonged economic downturn, that will make hard decisions easier for the more mobile people. We all gotta live.
I do like to see China succeed but I don't see how China can develop some semblance of U.S./U.K.'s academic culture (self-discipline, fairness, independence, etc.) in the foreseeable future. The shift requires a changing of the guards and that means 30 years and as noted before, it is a lot easier to retain and develop the talents locally than to ask people to return from abroad. Domestically, of course, financial incentives is a much bigger inducer if not the primary.
Right now the U.S. and China's national R&D spendings are about the same. When China is comfortably ahead (say by 2035), we will see China retaining much more of its top-notch people and even an influx of foreign nationals much like the U.S. today (like commercial pilots working for Chinese airlines today).
Taiwan's experience offers a glimpse when China can expect a reverse brain-drain. Outbound from 1960's to 1990's. Inbound from 1990's until the equilibrium is reached and people stop talking about brain-drains. What Taiwan doesn't possess is the size and breath of the world-class university and research opportunities that China can offer so China will do much better than Taiwan.
Data snapshot is a trailing indicator and shows off the U.S. well today but trend line bodes very well for China. Inertia is inherently hard to move and change quickly. No hurry.