So now that US companies have entered China, can you name some examples of first entrants who have “seized the market”?

I think your entire premise is dubious. The first mover advantage cannot be great because the Chinese government will never allow a foreign company to have a dominant position in an important domestic Chinese market. Without significant change since in government those first entrant companies are simply very foolishly assuming the regulatory environment will be anything like it is in the United States or Europe.