That's kind of hyperbole given the OP said "up to 10%".
But aside from that, don't a lot of billionaires (steve jobs, bill gates, etc) only pay themselves a $0 salary when they're rich and own their own company where they're paid in stock? So any % of $0 is still 0.
In the US RSU grants are treated as income. They literally show up on the W2 for the full value of the grant.
Of course an increased capital gains tax might capture the founders too, as would a wealth tax (though the latter would be very hard to administer on private companies due to uncertain valuation). The major preference in the current USA tax code is for investment income over earned income (including both W-2 income and some but not all small businesses, and including equity-based compensation except (sometimes) to the extent it appreciates), not rich over poor or poor over rich.