Stiff systems like whatever version of Communism the Chinese have now, with Emperor for Life Xi don't do as well with changing circumstances and the buildup their own internal contradictions as well as the flexible democracies so there is more than just China's demographic collapse in the equation.

Good point but it remains to be seen. China has seemed to look at the Soviets and 'improved' upon their design. At the same time the West has dove deeper into their downsides (corruption) with no improvement in sight. Does China really need to last forever or do they just need to outlast their rival?