I think you may have missed the background: US tax rhetoric -- he's doing what I think is pretty fair math with a fair take -- the math is supposed to break down what percent income tax you need to get the same dollars in tax revenue as a 1% wealth tax (on the wealthy). I think you could quibble with his risk free rate of return number, but most conservative planners would recommend a 4 - 5 % budget for risk free rate of return.

It's not about companies - it's about showing an equivalency between a Piketty-style tax of wealth setup and what we're used to thinking about in the US, an income-style tax setup on individuals.