Your hypothesis does not explain why the Chinese government is acquiescing to American trade demands. If they welcomed this economic slowdown they would be holding firm in trade negotiations.
What we are actually seeing happen is a rebalancing of foreign investment. American businesses have purchased stock in excess in the previous quarters using existing supply chains and are now moving supply chains out of China. Money that used to flow into China is now flowing into neighboring countries such as Vietnam. Mark my words, if the Chinese government allows this transfer to complete it will never come back to China and China's middle and lower class will be gutted.
Imagine if America's manufacturing economy was outsourced to China in the 60s rather than in the 90s when it already had a thriving service economy. That is what is happening in China.
Many people believe that authoritarian leaders are less beholden to their people than democratic leaders and because of this are able to withstand economic disasters easier. What they fail to realize is that when an authoritarian country fails economically there is only one group of people to blame and when judgement occurs it's not through polls but through violence.