They happen to be capitalist and they do produce a lot. But they don't produce a lot because they are capitalist. Those things have no clear relationship.
You or I could theorize about the causality, but I would say it's very hard to deny that there's a correlation. That's most of my argument here -- not philosophy, but how it seems like it works out in practice. The way it works in practice (evil capitalism producing better-run businesses than worker-owned factories with buy-in from everybody) actually doesn't make sense to me philosophically. I don't understand why capitalist systems + big-government intervention seem like they produce almost everything that needs producing in the modern world. I'm just saying that to me (and you may disagree), it seems like evidentially that's how it is.
Soviet Russia had industry. Soviet Russia had research and science. Soviet Russia made vaccines and was very prolific about vaccinating their population. Soviet Russia wasn't capitalist, or even communist for that matter. So how were they able to do that without capitalism? Everything that applies to Soviet Russia applies to China the same btw.
The Sinovac vaccine was very different from the Moderna vaccine -- it worked fine, but it wasn't the same step forward in vaccine technology. Soviet computing and heavy industry was far behind the West for the whole of the USSR. We didn't have millions of people dying of starvation, for one. I'm not saying command economies are always worse at everything than quasi-fascist-but-sorta-free-if-you-have-enough-money economies like the modern US. China in particular is better at solving certain types of governmental problems that tend to hamstring the US. But, you can't possibly be saying Soviet Russia was the equal of the West in terms of the well-being of their people. Are you?
If you're saying USSR and China don't count, what does count? Where has what you think would work better in the US been done on a big scale, and worked well? That's not some kind of rhetorical question, I really want to hear what the answer is.
So, clearly it has nothing to do with capitalism. And funny you mentioned the new deal. The last time the United States bucked capitalism for socialist policy. Republicans/fascists/capitalists were literally plotting to kill/overthrow FDR over his new deal policy. We literally didn't get there because of capitalism. We got there in spite of capitalism.
Yeah. That's what I mean -- I like Bernie Sanders, I like FDR even if some of the business leaders at the time thought he was Josef Stalin come to life in a wheelchair. That, to me, is a good economy. If that's not left enough for you and you want to go further, I think it's fair to ask where that system has worked well before I really agree that it'd be a good idea to completely overturn the US system in favor of it, that the result is clearly going to be better.