The point is all three were chiefly caused by Emperor Mao and His Personality Cult. I am trying to point out why having one single dude on top with all the power can wreak a lot of havoc.
I agree, in fact I think China has pretty much perfected the authoritarian model. Today the Emperor of China is the CPC itself. The CPC cannot be lobbied to favor any segment of the population unlike political parties in democratic systems, and with over 90 million members consisting of common folk, scientists, intellectuals, economists, doctors, intellectuals and businessmen, it has an unprecedented wealth of resources, experiences and knowledge to draw from. There is no entity better placed to be Emperor of China than the CPC.
Yeah, I am not betting on it. They are still very much a hermit kingdom and I think the Kim Dynasty is scared it will lose its grip on power if the country opens up and NK citizens start getting exposed to the outside world.
You're making the mistake of falling into the trap of seeing the world as democracies and autocracies. Both terms are actually very vague. There are actually far more political systems including universal suffrage democracy, republics, absolutist monarchies, feudal monarchies, aristocracies etc. A single party system like China, Vietnam, Taiwan before democratisation or Singapore is actually quite well described as a republic in which everyone can participate. Officials are promoted based on merit. The term People's Republic is pretty accurate.
North Korea is an absolutist monarchy. Officials are promoted based on the leader's favour. It's absurd to put it in the same category as China.
Democracy has a huge weakness in poor societies. You can buy votes. Democracy therefore fuels corruption. Officials are elected if they can buy enough votes and then proceed to extort those below them because they have to pay for the debts incurred when buying their position. This type of corruption of course also happens in monarchies and republics, but the act of voting makes this much worse. Look at African attempts at western style democracy for an illustration.
Another big weakness of democracies is that it polarises societies and destroys stability. Rich democracies may have a mechanism of removing a bad leader, but the democratic system is often responsible for getting a bad leader elected in the first place. Boris Johnson of Britain is one such example. He was elected because the people were given a choice between a bad candidate and one that was even worse. In a single party republic, someone like that would have never reached the top. Hitler was also elected. If Germany hadn't become a democracy after the first world war, there might not have been a second world war.
If you look at the evidence, it's politically stable systems that see the most progress. Europe's democracies during the industrial revolution were managed by kings and emperors, east Asia has experienced economic miracles under single party systems. Western style multi party democracy has crashed economic growth wherever it was introduced, including in Korea and Taiwan, the Philippines etc. Even the west is now suffering from democracy induced polarisation and instability while single party systems are much more united.