What you refer to as true capitalism, I am arguing is an idealist view. Idealist in this sense means not part of nor representing material reality. Marxist will claim the ideal form to not only not be present right now, but impossible to achieve due to the mechanics of capitalism itself.

We look at the process of capital accumulation through extraction of surplus labour power as self reinforcing. That means also that the contradictions within the system will reinforce unil reaching a break point.

As an example one could look at how capital consolidation leads to monopolies, how workers are impoverished to the point of not being able to buy the product of their own labour, or how the development of productionary forces lead to the developers, i.e. labourers, manufacture their own replacements.

These are the internal byproducts of capitalist mode of production itself. I have not even touched on the external contradictions happening through imperialism.

To make an analogy: If anyone were to claim that a drug was not actually medicine because it had negative side effects, we might both agree they were wrong. In my view, in the case of your idealist and my materialist view of capitalism, we disagree on the cause and effect in a similar manner.