Not trying to start an argument: what are examples the biggest successes of communist regimes/movements?

In China a notable example is the raising of the median income significantly, to almost 40k USD last I checked, essentially lifting a huge amount of people out of poverty.

The USSR raised life expectancy and HDI significantly, and when it collapsed both fell sharply in the resulting countries.

Was that income after Deng opened up China as the world’s manufactory? That giant amount of support from capital seems to be more effective than any decision communism made.
You cannot take that “support” out of the context of the decisions made by communists. Without the efforts made in “Mao-era” china, agriculture, industrialization, education, etc., the reform and opening up would likely have gone differently, china would probably look more like India and Brazil. And during (and after) reform and opening up, china actively steered the economy and set priorities, they continued to hold, as dessalines points out, the commanding heights of the economy, and used 5 year plans. So yes, you can say it was the “support” (capital) that came into china which made them richer, but only in context.