Those numbers assume that you believe in Uber's valuation. It's a winner's curse. Obviously, the equity is worth something, but $41B for a company that has pissed off regulators all over the globe and an unlikeable founder seems high. Then you have the uncertainty around vesting, weird acquisition terms, preferences, whether you believe the valuation, etc. It's impossible to come up a fair value for the equity without knowing a lot of things that average engineers will never have access to.
$170k + $500k of paper as valued by VCs (who have a different risk profile, and get the bonus of being able to inject their buddies into executive roles) is not the same thing as $670k. Also, Uber is a company that everyone hates and it has to pay an "asshole tax" to be able to hire anyone.