It's completely plausible that a nation with a wealth of natural resources but an economic system that treats people terribly could win a series of wars and establish its economic system as the dominant one in the world, and then use its power to maintain status quo.

A marketplace of ideas does not necessarily lead to the best outcomes, or even good outcomes.

Suppose the marketplace of ideas is an unregulated marketplace. Then the wealthy and powerful can use their wealth and power to determine the world that other people see, getting those people to mistakenly fight for things that help the wealthy and powerful.

But suppose it's kept a fair marketplace. Fairness is not natural – it's a human value that we have to actively maintain. But suppose we succeed. Even then, the marketplace may not select the best ideas, because people have emotional needs – like belonging to community – that will cause them to stubbornly reject good ideas. But we accept this because it's the only way for us to live with each other; if I want you to let me disagree with you, I have to let you disagree with me.* The price of intellectual freedom is very, very steep, even if it's worth it.

So I don't believe the fact that capitalism is dominant is good evidence that it's the best idea so far. In fact, I think we have little evidence of it at all.

* There are of course complications of the Popperian, paradox-of-tolerance sort, where we do have to fight to the death, so to speak. If someone repeatedly demonstrates an unwillingness to compromise or act fairly, they've left you the choice of letting yourself perish or eliminating them, which is a shitty situation to be in.