I think this is in contrast to highly automated industries (tentatively). I think the train of thought is that lower labor costs results in a higher concentration of wealth as less wealth is distributed since there are lower labor costs.
However, I would posit that the more direct measure is profit percentages. Hypothetically, if labor costs go down, and profit margins stay the same (ie if the savings are passed on to consumers), then I would imagine there would be an increase in consumption.
Where the money gets back to workers may change (as increased consumption would mean increased demand for the materials McDonalds uses, which likely have higher labor costs). High profit percentages, however, typically benefit those that own some of the company.
This is entirely conjecture, I am not well versed in economics. If there is some flaw in this (and I'm sure there are several), I would love to be corrected for my own education!
I reject mercantilistic views of economy. They belong in the 1600s where they died.
I'm pretty comfortable abandoning the view. It wasn't built on a strong basis.
Honestly, income inequality is a red herring of left politics and public schooling. If the most prosperous societies have high income inequality, then the question must be asked: does it matter?
Unless you want to design a utopia. That goes swimmingly every time, I promise.
Edit: If income inequality is a consequence of freedom, it's a very, very tiny price to pay. Don't optimize for the economy. Optimize for freedom. Empirically, that's how you create prosperity.