I can’t get past your assumption that there are economic options called capitalism and socialism, although I understand you are firmly hitched to the dominant mythos of the Cold War.
Seems to me that every country on the face of this planet has a mixed economy with the possible exception of North Korea, where we don’t know enough about the economy to evaluate Kim’s claim that it is socialist.
During the Cold War, the Second World was more socialist than the First World was capitalist, but the purists didn’t do well. We don’t look back on Stalin or Mao as economic prodigies.
You assert that a mixed economy cannot exist but I would like to hear of a nation where a mixed economy does not exist. Even Cuba has stirred in a dab of capitalism.
So, what do I claim the Cold War was about? Democracy v. Autocracy. And they really are like oil and water because an autocracy bleeds population. Everybody not in the autocrat’s immediate circle wants to leave. There’s never a shortage of would-be autocrats, but they are seldom able to manage a peaceful transition of power. Power struggles and brain drain eat them from the inside.