I feel this discussion always misses an important point. The value of something has nothing to do with its costs or profits. The value of things (labor included) is subjective and is normally related to its scarcity. In the period analyzed the workforce basically doubled because the inclusion of woman to the workforce, therefore it had a huge pressure to keep it low.
If the productivity of less-skilled workers has not kept pace with average productivity, this was by design. It was not the fault of these workers; it was the fault of those who designed policies that had the effect of devaluing their skills. From Baker's article.
my point is that the value of the work is not directly related with its productivity but with its availability, which doubled during the last few decades.