The reason China is lasting for a longer amount of time than the USSR has to do with the fact that they made a compromise on their views, they accepted that it was impossible for them to remain 100% communist and they accepted a little bit of capitalism in order to survive, but they are not realizing that even that small amount of capitalism is going to be enough to bring China down.
In a way this is very similar to what happened to Sparta and Athens, Sparta was obsessed with maintaining their society just as it was and when they finally beat Athens they thought that everything was going to be fine but then the cultural and economic freedom of Athens got all over Sparta like a virus eventually causing its fall, and I expect something similar to happen to China.
I don't agree with any of the points you have posted here. The economic system in China is almost 100% capitalist. They moved away from the failed socialist system many decades ago (after watching what happened in the former USSR). Until the 1980s, China was both authoritarian and socialist. Now China is authoritarian and capitalist. And this is the most successful political system.
Democracy has failed all over the world. The democratic governments need to increase their handouts and freebie distribution every year to remain in power and this has meant that in almost all of the democracies, the federal debt is now more than 100% of the GDP. This is not a viable scenario in the long term. China on the other hand has managed to remain free of the debt-trap, even with very low tax levels.
this could also be the reason why China is investing everywhere like in Africa to Europe to which they have done so for almost 20 years now. they couldn't just spend their money to build infrastructures around the depressed area in China because they need more money coming into them and to realize this, they need the belt and road. the silk road of old times where they can trade to the outside world.
true they are capitalist now but they don't have all the resources, this is even the reason why they want Taiwan back to join the mainland. they grab contested islands in SCS because they needed all these resources not just for military force.