Bravo for this. My experience is with capitalism, I have not spent much time studying Marxist economics. I can't vouch for the truth of this analysis, but it makes sense and is nicely laid out and very educational. Two statements stuck out to me:

"But as those economists frequently point out, their models are not supposed to mirror reality. They are just supposed to simplify reality enough to make predictions." This alludes to a problem economists have explaining their theories: most econonomics deliberately avoids norms, either personal or societal. It assumes people act rationally according to their own desires, and essentially tucks norms into the demand curve. But after a theory is developed, it is almost universally acknowledged that norms can produce exceptions, or even alter the original equations.

For example, economics can show clearly that a Jewish man living in Ames, Iowa, or Lincoln, Nebraska will likely marry for the first time later than a similar Jewish man living in Brooklyn. That is because the marginal cost of finding a Jewish bride in Nebraska is much higher than in Brooklyn. Variance can change that in individual cases, but on average that is the theory. But the man in Nebraska could also fall in love with a Catholic woman and marry earlier. Economics does not do love, or human emotions, very well.

The second statement: "While it is possible to make useful theories on the basis of assumptions, I would argue that there is a limit to how arbitrary those assumptions can be. I would argue that those assumptions need to be independently justifiable for us to be confident that our theory reflects reality at all."

This is critical. Most people think of capitalism as competition. But competition is not a definition of capitalism, only one kind of capitalism. The theory of perfect competition can prove - verbally, via graphs, and mathematically - that competition produces the optimum amount of a product desired, at the lowest price, with the most efficiency, and long term profits are zero. But - and this is a big but - the theory makes several important assumptions as prerequisites for it to work - such as perfect information between producer and consumer, perfect freedom of entry and exit of firms, homogeneous products, lack of discrimination, etc. Many of these assumptions are violated in most markets. Where many of them hold - go to a farmer's market for example, or with consumer electronics - competition produces great results.

But our economy is becoming increasingly concentrated, and monopoly economics is becoming the dominant system in America and much of the developed world. A monopolist or oligopolist has market power, meaning they can set the level of output and price to maximize profit, which can't happen in a competitive market. This is not bad per se, but can lead to market distortions that enrich a few monopolists at the expense of consumers.

Also keep this in mind - when you hear politicians or even many economists today talk about a "free market", they are not talking about free competition, what they mean is lack of government interference with the workings of the market, which they deem necessary to maximize profits. But a lack of government control in a monopolistic market both encourages further concentration, and prevents reining in the excesses of unfettered capitalism.