China wants the Washington-led neoliberal consensus to persist. Both the US and China have benefited tremendously from such an arrangement at the expense of the entire world.
Hard truths. I'll always defend China against western imperialist propaganda, but your metaphor of a toxic relationship seems quite fitting.
I also don't enjoy reading again and again so many different and partially contradictory variations of the "China is playing the very long game" argument. There might be a lot of truth to that, sure, but we can't really know in every case what the rational is. It's also a very easy way to speculate and pull out of a hat new justifications for almost every concrete action. What a lucky coincidence for Chinese and US capitalist, that all the very different long term strategies China is said to pursue usually favour capital in the mid term.
Also long-term arguments can always be turned around to the past. The US empire wouldn't have survived this long if Nixon hadn't gone to China to make a deal. Global capitalism might not have survived the financial crisis of 2007/2008 without China jumping in with the biggest government spending program ever to prop up demand. Iran is forced to attack the harbor in Haifa, that China built. If rumors about Pakistan drawing a red line and threatening nuclear retaliation in case US/Israel escalate beyond a certain point, can have an effect, than just imagine how effortlessly a single short statement from China could have lessened Palestinian suffering.
Yay! Go PSL!