Salary is always lower than the (expected) value of work. If the value of work was equal to salary, the employer would have to reason to do this transaction.
At the margin, they are all equal because trade continues until the gains from trade are exhausted.
In many countries and U.S. states, laws guarantee that the cost of an employee to an employer is almost twice as much as what the employee is paid. In those circumstances, the potential gains from bilateral trade are not exhausted and people engage in that trade outside of the dominion of the state.
But if you're just the average developer, like most of us really are - the higher competition will surely make it harder to negotiate higher pay.
This might be true at the lower end close to minimum wage, but payroll taxes are a specific % (usually around 15% at the federal level, and the employee pays about half that) and insurance and other benefits are typically a fixed cost per head (15k to 30k per year at most of the places I've worked). The only thing that might be variable are things like 401k match. Once you get to six figure salaries, the fully loaded cost per employee is 120-130% of their salary.