So do I think minimum wage earners are contributing NO MORE to the profits than they were 20 years ago in constant dollars?
I can see that they ARE contributing more. They are making more widgets at lower cost and corporate profits are going up. They are working faster, they are working smarter. They are learning new tools of automation and process control. They are discerning more in their inspections, and operating more complex measurement equipment. This allows the company to make a higher margin. Earn more money - more profit.
You're overlooking the real change here--they have better tools. It's not that the workers are making more, it's their tools are making more.
If that value goes to the worker instead of the owner of the tool there's no point in spending the money on the better tools and there would be no progress. You're being a luddite here.