You're essentially making a Marxist argument using many of the same premises Marx and later Marxists used. I actually had to do some research to respond to this because I wanted to make sure I wasn't misunderstanding the argument. But I have to admit, I do wonder whether you actually wrote this yourself.
Normally, I would start by defining the terminology you're using: liberalism, capitalism, socialism, etc. But I'm not going to do that here. I don't think getting bogged down in definitions is going to resolve the fundamental disagreement, because I think we're operating from completely different assumptions about how these systems actually function.
I could obviously be wrong. Maybe you're an economics professor at Harvard and I'm completely out of my depth here. Somehow, I doubt it, though.
So instead, I'll counter the broader argument with one word: history.
Marx and the other early socialist and communist theorists identified some very real problems with capitalism. Their criticisms of concentrated wealth, class power, exploitation, and the political influence of capital are not inherently irrational. In fact, many of those criticisms remain relevant. The problem is that the theoretical solution has repeatedly run into the same obstacle: human beings.
The historical record does not demonstrate that attempts to replace capitalism with comprehensive systems of collective ownership have produced the stable, classless societies Marx envisioned. Whatever the theoretical merits of the argument, the practical results have repeatedly been far more complicated.
Meanwhile, some of the world's most prosperous democracies have developed in the opposite direction: capitalist economies combined with democratic institutions, extensive welfare states, strong labor protections, taxation, and significant regulation. The Nordic countries are probably the clearest examples. The OECD itself classifies the Nordic countries within the social-democratic welfare-state tradition, while still describing them as developed capitalist economies.
China is an interesting example from the other end of the spectrum, although I wouldn't describe it simply as "socialism." China officially describes its system as a socialist market economy, with substantial state and collective ownership alongside extensive private economic activity and legally protected private property.
So ultimately, I don't actually disagree with the fundamental observation that there is a tension between concentrated economic power and democratic political equality. That's a legitimate problem, and I think democratic institutions absolutely need mechanisms capable of preventing economic power from becoming political domination.
Where we disagree is what follows from that observation.
I think Marx's critique identifies a real structural problem, but I don't think the historical evidence demonstrates that abolishing private ownership of the means of production is the necessary solution. In practice, the systems that have proven most durable have generally been mixed systems: markets and private property combined with democratic government, regulation, redistribution, social insurance, and public institutions.
And perhaps the deeper problem with Marx's theoretical framework is that it assumes we can fundamentally restructure the economic system without having to account for the behavior of the human beings operating it. Until scarcity itself is substantially reduced, I don't see a realistic path toward the kind of society Marx envisioned.