You owe the same amount in income taxes regardless of whether you're paid in stock or cash.

I think you're confusing this with the case where founders or early employees own large amounts of stock that they received early on in the company. They paid little to no taxes when they received it because it was worth basically nothing at the time. Later, the company has grown and it's worth a lot, so they have a large unrealized gain that they can use as collateral for loans. But that certainly wasn't guaranteed to happen. Most startups fail.

Don't you pay taxes on those when they vest?