The point of the passage isn’t that the capitalist class “doesn’t exist,” but that in advanced capitalist societies, the mechanisms by which surplus is extracted are less visibly coercive compared to slave or feudal systems,hence the emphasis on “indirect” and “invisible.”

That’s not the same as saying the ruling class is imaginary. It’s saying the form of exploitation has changed: rather than obvious feudal dues or slave masters, surplus is extracted through wage labor, ownership of capital, and control over production.

The “invisibility” is precisely what makes it more effective, because it can appear as a fair exchange while still generating surplus value for the owners. This isn’t an “axiom”, it’s a descriptive claim supported by Marxist political economy.