It's literally the basis for Thomas Piketty's 'Capital in the Twenty-First Century'. It's a dense book, but widely acclaimed. It was also published 8 years ago and the claims aren't controversial.
To say it's not controversial seems misleading. It may be widely acclaimed, but also hugely criticised. Wikipedia has a short collection of the criticism.
There are very few critiques of the empirical assertion that the capital share of the economy is not increasing, though. Most are on other parts of his thesis or argument.
https://en.wikipedia.org/wiki/Capital_in_the_Twenty-First_Ce...