The assumption of capitalist-like structures is for a good reason. Because there is literally zero practical evidence that scarcity can exist without them in scalable economies. If you require scalability in the presence of scarcity, you will have markets, you will have currency, you will have competition, you will have investment, and so forth. At best these things can be mediated by centrally planned state capitalism. But pretending like this is not just another brand of harm reduction capitalism is rhetorically counterproductive.

The overwhelming consensus of the past century regarding Marxist economic theory is that it is incomplete at best because it takes a very naive view of scarcity. Where Marx requires revolution and then a bunch of hand waving, modern revisionism requires harm reduction and the gradual whittling down of scarcity over time. Historical materialism is certainly a pretty useful economic lens, but Marx really goes off the rails in the prescriptive conclusions he draws from that analytical framework.