France Payroll tax: 20% for salaries over €151,965.
USA Income tax: 42%, including State (CA) and Federal, excluding deductions
France Income Tax: 50%.
So the labour cost will be a lot higher due to payroll taxes, and the employee will take home less due to income taxes. High VAT (20% in France, 8.5% in SF) means consumer purchases are also more expensive. If you are in Paris, you're at a latitude 48.8N, SF 37.7N.
The same is true for moving to other Anglo countries: UK, Canada, Australia have similar lower-tax regimes.
France, Germany etc. are charging huge payroll, income and sales taxes to fund their huge welfare states and bureaucracies, but in the process ruining their competitiveness.