Is the ACP's notion of value centuries behind current economic tought?

Is value subjective? Is value derived from the labor going into a good or service? Do business owners exploit their employee by stealing their "surplus value"? Why do diamonds cost more than water while water is necessary for life?

The value theory of value was promoted by David Ricardo and bought into and popularized by Karl Marx.

However, in the late 19th century three economists developed economic theory that became known as the marginal revolution. Value,they said was not something inherent in the object but value results from the subjective evaluation of the person and that evaluation is made at the margin. For example, if you have 20 apples you are likely to value the 21st apple less.