Read the article I linked above for the answer. Richer countries like the US and western europe industrialized at least a hundred years before. Both the USSR and PRC were largely feudal economies in the early 1900s. But the soviet union (despite starting out from about the same point as Brazil in 1920) caught up to the US within a few decades, beating it to space, and forcing it to allocate tonsof resources to state-run research and development projects.

It wasn't even really the USSR's choice to de-link, it was heavily attacked by all the western countries during it's civil war, and they embargoed the country when they lost. The west rode their hundred-year head start on industrialization and resource advantage from hundreds of years from colonialism and slavery, and also funded the newly defeated fascist countries like germany and japan to become anti-communist bulwarks producing consumer goods.

The PRC has now surpassed the US in most tech sectors, once again proving the superiority of socialism.

You're comparing 300 million and 1500 million people to the entire rest of the world. And in that rest of the world is about 1000 million people with significantly better living conditions, infrastructure, institutions and education, who of course have huge advantages in being able to create advanced technologies.

And even then you're ignoring that there are industries where the Soviet Union and China both managed to become world leaders.

Another thing I thought of randomly: read cj chivers the gun, which compares the development processes of the ak47 vs the ar15, and their histories. It's a microcosm of the superiority of socialist / collective planning vs the shitshow of capitalist profit-driven development.