Some portion of that suffering was thanks to capitalist ideologues who actively worked to undermine the success of alternative systems. We don’t really know how well other systems work in the modern world because we haven’t really given any of them a fair shake.

A successful system is robust to tampering from external and internal actors.

by that logic, US democracy and capitalism arent successful either (see Russian election tampering and OPEC influence on US/global economy)

And yet, the US and capitalism are both still around, and their continued existence ensures we don't get people in comments sections claiming that we don't know how capitalism works as a system because _real_ capitalism still hasn't been tried.

This is like the spiderman meme where they're all pointing at each other. One flavor of capitalism fights another, is it any surprise that a capitalist wins or that the overall result is a strengthening of the military-industrial complex due to increased defense spending?

How about a more interesting question. Do you believe capitalism is the best or most just way to organize an economy which is possible, that it is "the end of history?" Do you think on an infinite timeline, assuming no extinction of the species or any other confounding factors, humanity will never come up with a better way to organize our economy?

Given what the US did to the socialist South American states in Operation Condor, this is equivalent to "might makes right," which is no good basis for a political system.

Andre the Giant wasn't such a tough guy as a newborn, but that doesn't mean I could've wrestled him at his prime.

This is a Just So Story. "The fact that we won proves that we deserved to win." You can do better.