Income (or revenue), what is left over freom the paycheque (profits) and net worth (market cap) - applying a simple ratio to companies of revenue to market cap doesnt work, why would applying a simple ratio of income to net worth for people who live hand to mouth and billionaires work any better.
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.