You should know that most Marxists believe capitalism is an economic engine unlike anything that came before it. That doesn’t mean we can’t build a more rational system. If we wanted to approach the problem scientifically we would study capitalism, understand how it works and came to be, form hypotheses for how to build something better, and then experiment.

I’d also add that the formation of the modern government, ie liberal democratic states, and the development of capitalism are one and the same. Our totalizing market economy can not exist without governments ensuring conditions are right for market exchange to operate smoothly. As such, I don’t think it’s possible to say a failure of governments are not a failure of capitalism. It’s a package deal so to speak.

It’s not a failure of government when the government effectively serves the ruling class (i.e capitalists). It’s a feature, not a bug.