There's actually very little written by Marx or Engels on any kind of proposed "cure". Marx himself reacted very negatively to the idea of "writing recipes for cook-shops of the future." He didn't think it possible, nor desirable, to draw up plans.
The "cures" in the 20th century were on the whole written by people with far simpler minds and uglier motives. Their actions don't take away from the value of Marx as an analyst and critic of capitalism.
What little they did write in the Manifesto did plenty of damage all on its own, and it served as a step-by-step guide for most of history's failed communist states. (Particularly the bits of making "despotic inroads" on the existing systems)
I don't disagree, but I also think much has been lost in translation between 19th century phrases and language and conventions vs now. Context of the time was revolutions in the context of a mix of brutal 19th century monarchies/dictatorships, proto-capitalist/mostly agrarian economies, and brutal badly regulated industrial capitalisms.
The phrase "dictatorship of the proletariat" in particular has a very unfortunate history and ... interpretation.
The "cures" in the 20th century were on the whole written by people with far simpler minds and uglier motives. Their actions don't take away from the value of Marx as an analyst and critic of capitalism.