PRC is capitalism with some controls.

The CPC’s controls on capitalism are enormous, and the bourgeoisie are largely excluded from the political sphere. Previously.

Cuba is a dictatorship of Castro family. […] DPRK is dictatorship.

China, Cuba, the DPRK, Laos, and Vietnam all have a form of Marxist-Leninist democratic centralism, as every communist country so far has, AFAIK. Cuba’s current president isn’t related to Castro.

This certainly isn't a Marxist take, at the very least.

Calling the PRC "Capitalist with controls" implies that private ownership is the principle aspect of its economy, when in reality the overwhelming majority of its large firms and key industries are in the public sector as the private is made up of small firms, sole proprietorships, and cooperatives. Here's a handy infographic:

The PRC's economy is classically Marxist, as Marx didn't think you could abolish private property by making it illegal, but by developing out of it. Socialism and Communism, for Marx, were about analyzing and harnessing the natural laws of economics moving towards centralization, so as to democratize it and produce in the interests of all. This wasn't about decentralization, but centralization.

Markets themselves are not Capitalism, just like public ownership itself is not Socialist. The US is not Socialist just because it has a post-office, just like the PRC is not Capitalist just because it has some degree of private ownership. Rather, Marx believed you can't just make private property illegal, but must develop out of it, as markets create large firms, and large firms work best with central planning:

The proletariat will use its political supremacy to wrest, by degrees, all capital from the bourgeoisie, to centralise all instruments of production in the hands of the State, i. e., of the proletariat organised as the ruling class; and to increase the total of productive forces as rapidly as possible.

I want you to look at the bolded word. Why did Marx say by degree? Did he think on day 1, businesses named A-C are nationalized, day 2 businesses D-E, etc etc? No. Marx believed that it is through nationalizing of the large firms that would be done immediately, and gradually as the small firms develop, they too can be folded into the public sector. The path to eliminated Private Property isn't to make it illegal, but to develop out of it.

The essential condition for the existence, and for the sway of the bourgeois class, is the formation and augmentation of capital;[43] the condition for capital is wage-labour. Wage-labour rests exclusively on competition between the labourers. The advance of industry, whose involuntary promoter is the bourgeoisie, replaces the isolation of the labourers, due to competition, by their revolutionary combination, due to association. The development of Modern Industry, therefore, cuts from under its feet the very foundation on which the bourgeoisie produces and appropriates products. What the bourgeoisie, therefore, produces, above all, are its own grave-diggers. Its fall and the victory of the proletariat are equally inevitable.

This is why, in the previous paragraph, Marx described public seizure in degrees, but raising the level of the productive forces as rapidly as possible.

China does have Billionaires, but these billionaires do not control key industries, nor vast megacorps. The number of billionaires is actually shrinking in the last few years. Instead, large firms and key industries are publicly owned, and small firms are privately owned. This is Marxism.

The USSR was Socialist, and it was dissolved for a variety of reasons. It would take volumes to discuss, but I recommend Blackshirts and Reds.

The current democratically elected President of Cuba is Miguel Díaz-Canel, so not sure where you got your Cuba talking point from. We aren't in the 90s anymore, and even if we were, the Cuban people still supported the Castro family and the Socialist system regardless.

Vietnam is Socialist, and has a similarly classical Marxist understanding of economics as the PRC. You're correct that it has a very similar structure, but wrong in thinking it's a betrayal of Socialism. Rather, I recommend reading Marx, I'll include a reading list at the end.

The DPRK is less of a dictatorship than the US, its governed by 3 parties overall and has more of a participatory election system. I recommend reading this article on the DPRK.

Your second paragraph starts off fairly strong! You're correct in the idea that full socialization of the economy requires vast development of the productive forces, but you quickly derail. You acknowledge that no system is pure, a key principle in Dialectical Materialism, but make the error of assuming contradictions, which are in all systems, are the defining aspects, rather than the principle elements. I went over this above.

Further, you make the error in stating that a vanguard is to "relinquish power." This is wrong. First, it implies Vanguards as distinct from the Working Class, and not its most advanced elements, and further it implies that Vanguards are meant to disappear before Communism, a global, fully publicly owned economy, is achieved. On the contrary, a vanguard can only disappear when there no longer are advanced, backwards, and general sections of the working class, and class in general has been abolished, which requires Communism to be achieved to begin with.

Moreover, you answer this with the distinctly Anti-Marxist notion that decentralization is the answer. Perhaps if you are an Anarchist, I can understand your critique, but if you're attempting to uphold Marx, he would disagree firmly. The advancement of industry requires the management and administration of industry. Government will remain even when the state has whithered, in fact we will only ever get more centralized. This does not go against democracy, however, it extends it by extending the reach of the voice of the workers.

I recommed checking out this introductory Marxist-Leninist Reading List I made, and if you have specific questions, I'll do my best to help answer!

Cuba is a dictatorship of Castro family.

Who is the current president of Cuba?