"Labor’s share of national income—that is, the amount of GDP paid out in wages, salaries, and benefits—has been declining in developed and, to a lesser extent, emerging economies since the 1980s."
https://www.mckinsey.com/featured-insights/employment-and-gr...
This divergence since 1980 is the subject of Picketty's Capital in the 21st Century.
But the extra has gone to land, not capital.
Piketty fails to make that distinction. See eg https://www.forbes.com/sites/chuckdevore/2015/07/22/piketty-... or https://www.brookings.edu/bpea-articles/deciphering-the-fall...
If it's all gone to land, the situation seems worse as far as inequality goes. The top 1% of households own 40% of land in the US as of 2017. The next 9 percent own 42%.
So maybe it's inexact to call it "capital" vs. "labor", but... a class of people is dominating.
Not sure about 'class'.
But the policy implications are quite different:
Land value taxation can capture all that extra rent going to land without hurting the economy one bit. See https://en.wikipedia.org/wiki/Land_value_tax
By contrast, taxing capital is a really bad idea. Eg capital gains taxes hamper productivity growth.