Yeah, the downfall of communism/socialism had nothing to do with pressure from foreign powers, or sanctions or coups or anything like that. Gorbachev is responsible for the dissolution of the USSR, and the World Bank and IMF are responsible for liberalizing former socialist economies. Those two institutions are responsible for the globalization of capital and the continued exploitation of the global south.
If people are escaping communist governments it is because of political repression and authoritarianism. The services they provide are actually very beneficial; China has reduced poverty impressively (Vietnam has poverty decreasing steadily annually as well) and Cuba guarantees health services to all its citizens, and even has a higher literacy rate than the United States. Marx never said a dictatorship of the proletariat should be realized through a vanguard party, or a one-party stronghold over the country, that was Lenin. Most communist governments since the inception of the USSR have been modeled after Marxism-Leninism.
I would argue that capitalism is unsustainable, as literally every 4 to 7 years there is a recession, sometimes a depression. Capitalism is kept alive by the governments that continue to bail it out. In the direction that capitalism is going, greater profits gained by the wealthiest elites while more people are thrown into poverty, there is growing income inequality in all capitalist economies and especially in the United States, a middle class barely distinguishable from the working class. Capitalism is not sustainable for working people, period.