[legitster]

This is misleading. Adam Smith presented this as a possible solution to an economic paradox at the time. But later philosophers came up with much better solutions:

https://en.wikipedia.org/wiki/Paradox_of_value

There's no reason to believe that Smith wouldn't have latched onto the much better solution. So being hell-bent on the incomplete answer from the 1700s is a unique peculiarity of Marxist theory.

[consilient]

> But later philosophers came up with much better solutions

Yes, later than both Smith and Marx. Marginalism didn't go mainstream until the 1890s, though the necessary pieces were there waiting to be assembled from about 1870.