According to Karl Marx, laborers really produced all wealth, and the business owners (capitalists) were the recipients of the wealth in the form of profits.

This is true.

Explanation:

Marxist theory follows David Ricardo's labor theory, stating that human labor is the source of value. The capitalist does not pay workers for the full added value of the good produces, he only pays them a salary for subsistence. What remains is surplus labor and it creates surplus value. The capitalist takes his profit from this surplus value. Thus he exploits workers.