No its not a huge gain for China.

China's government is still a dictatorship and compared to the US, China still lacks the basic legal framework and intellectual property laws that make the US the world's economic leader.  China's government sets trade agreements strictly for China's benefit and weak intellectual property laws give little protection to foreign companies.  Everything is done on China's terms.  China's government also competes unfairly through state-owned companies.

Countries do business with China because of China's huge population, not because China is great place to do business. The fact is, most countries don't trust China's government on trade and China will not be a leader until they modernize their laws and approach.