You directly tied vaccines, supermarkets, and computers to "massive, organized economies" and tied that to Capitalism, so if I misunderstood what you meant by that then fair enough. However, what follows in your comment is not evidence for belief in superiority of one economic system over the other.

Your first major paragraph talks about how, in your vision, highly developed countries tend to be Capitalist, while despite the obvious benefits of Worker Co-operatives, they seem to be rare in these developed countries. I'll answer each bit individually.

Capitalism is a system of exploitation, whereby owners suck up the value workers create. As the world gets increasingly complex, the farther away from the top you are, the more exploited you are. In the modern era, this expresses in totally imperialist control of the global south. Nestle, for example, uses child labor and brutal working conditions to extract necessary resources and profit immensely, despite being headquartered in Nordic Countries, where the quality of life and development are some of the highest in the world. This is by no means an exception, it's the rule.

What drives quality of life is not what economic system you have, but the level of development, largely. Reducing disparity is fantastic as well, but primarily, development determines quality of life. Tying supermarkets, vaccines, and computers to Capitalism, rather than to developed nations, is a bit of a misattribution: The tools and goods present in a country do not care who owns tools, all they care about is investment in industrialization and development.

As for why Worker Co-operatives are not more common, it's fairly simple. Despite being more stable than Capitalist entities, and providing greater worker satisfaction, Co-operatives are more difficult to start than Capitalist entities. As we have previously discussed, it is in Capitalist's interest to keep it that way, and prevent the system from incentivizing these better structures, so that they can maintain power.

Next up, your request for a "specific example" at a country-scale of what I am asking for. The shortest answer is that there isn't one, at least not yet, but that by no means discounts the possibility of its existence in the future, you'd have to explain why you think it impossible. The longer answer is that there have been several examples with radically different structures that modern leftists have all learned from, but none of which were 1 to 1 what leftists seek to replicate. What do I mean? Well, some examples include the EZLN and Revolutionary Catalonia, which are/were Libertarian Socialist and Anarcho-Communist, respectively. They have their own shortcomings, notably the modern lack of existence of Revolutionary Catalonia due to its inability to defend itself, and the EZLN for being very slow at developing, though it works for the people who live there.

There are other examples of more statist countries, organized along the lines of Marxism-Leninism. These include places like Cuba, the USSR, and China. While the latter 2 did manage to skyrocket quality of life with huge investments into development, ultimately the Politburo is unaccountable to the masses, and as such the governments of each have committed atrocities. Cuba is a bit of a unique case, it's nearly completely locked out of global trade, and as such it has had severely stunted development.

So far, I wish to recreate none of those examples, but each has provided extremely valuable information on how to build a future Socialist society. You appear to be rejecting the idea of analyzing the mechanics of Socialism and Capitalism and applying the results of that analysis to the real world, and instead you appear to be in favor of simply "copying whatever country has a higher quality of life," without looking at trends or cost. Again, leftist believe that Capitalism itself is unsustainable and brutal, and therefore needs to be replaced with Socialism. This is not because of vibes, but genuine mechanical analysis.

I have a question for you, if you'll oblige: what is the extent to which you have read leftist theoretical texts, such as from Marx, or even Anarchists like Kropotkin? If none, would you be willing to read?

You or I could theorize about the causality, but I would say it’s very hard to deny that there’s a correlation.

You've yet to point out any correlation. I specifically pointed out how there is no correlation. Which you just ignored or hand waved away completely.

The Sinovac vaccine was very different from the Moderna vaccine

Yes but it's hard to know where to start with the problems with this statement. First that's not a creation of the Soviet Union since it hasn't existed since the early 90's. Further the efficacy of a vaccine is non sequitur. You said it was capitalism that gave us vaccines. Yet non capitalistic systems make them too. So you move goalposts claiming they aren't as effective. If you're going to make an argument stick to it.

Soviet computing and heavy industry was far behind the West for the whole of the USSR

Again not relevant. They shouldn't have had any at all if it was capitalism that gave them to us. The fact they were making their own in any capacity disproves your statement.

We didn’t have millions of people dying of starvation, for one.

At that exact moment? Maybe not. We've had our own famines however. And starved an uncounted number of people. Even then, those famines were not caused because communism. They had nothing to do with communism. They were naturally occurring famines. Made worse by unanswerable ignorant authoritarian leaders. Unwilling to listen to actual experts or those with experience. It had nothing to do with any actual social or economic policy inherant to socialism/comunism. But if you disagree please point out where in Marx's writing the fault lies. Engles is a spiteful lunatic who's musings and philosophy have caused untold damage to the ideology as a whole. But even his philosophy didn't cause the famines. But if you disagree please explain how "because communism".

If you’re saying USSR and China don’t count, what does count?

I'm not saying that. They do. Naming something Communism or Communist doesn't make it that. There are specific points that make something communism. Which none of those countries really have had. Specifically they're Marxist-Leninist. Though Lenin's ideology runs counter to a lot of Marx's. Making that label an oxymoron more than anything. Regardless, marxist-leninism wasn't and still isn't communism. It's goal was to develop the infrastructure to the point that somehow. Through hand wavy magic the powerful autocrats in charge would magically give up their power and control, switching everything to communism when the time was right. Yes, it's stupid magical, and irrational thinking. But not communism

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.

Most the rest of the industrialized world. No really. Most have single payer. It works well. Scandanavian taxation, regulation, and governing philosophy. It's not perfect, but far better than what we have in the US. Not to mention their public central heating. Austrian style public housing. It's comfortable, affordable, and many of their celebrities even choose to live in it even. Public high speed rail and mass transit like Europe and much of the rest of the industrialized world. The sort of stuff capitalists and capitalism keep us from. Not because they don't work. But because there's no money in it for them.