I think we agree that labor is a source of value - discovering, creating, transforming inputs to add value - and capital is surplus value from previous labor.
I think we disagree that socially necessary hours of labor is a useful "objective measure" of the value of the product.
I think too many variables have to be hand-waved away by that "socially necessary" qualifier, such that it completely hides any value (ahem) of the measure.
We've identified that we have to qualify socially necessary labor hours by
- average skill and diligence of the workers currently available in the region
- efficiency of the production processes for this item and all capital goods and materials used in production
- level of technological advancement for all of the above
- availability of competing products
That's a very abstract measure casually described as hours of labor, and seems to have little descriptive power, much less predictive power to help decide what will be worth producing. Frankly, I'm not sure if it can be calculated at all for any commercial product.
"The value of a commodity can be objectively measured by the hours of socially necessary labor required to produce it."
Can anyone cite the hours of socially necessary labor required to produce any single product? (See "I, pencil" for an example of the complexity)