The measure to look at is consumption inequality, not wealth inequality. It has also increased (though it is harder to measure than income inequality, but see https://www.nber.org/papers/w17982.pdf), but the progressive global wealth tax of up to 2% advocated by Piketty in Capital in the Twenty-First Century could increase consumption inequality instead of diminishing it, and is otherwise less efficient than a tax on consumption.

See “Measuring inequality: A three-headed hydra”[1] in The Economist and “Economics is all about consumption” by Scott Sumner.[2]

[1]: https://www.economist.com/blogs/freeexchange/2014/07/measuri...

[2]: http://econlog.econlib.org/archives/2014/07/economics_is_al....