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.