On the same 65 000 € gross, a worker takes home roughly CHF 18'230 more per year in Switzerland than in France. That gap reflects the tax structure alone — before rent, healthcare, or savings behaviour come into play.
Housing is the first multiplier. Switzerland has very high rent pressure, while France has high rent pressure. That means part of the higher take-home in Switzerland can be absorbed by rent if you land in a major city.
Healthcare and pensions go in the opposite direction. Switzerland runs a public healthcare model — Mandatory private health insurance (~CHF 350+/month) outside payroll. France uses a universal model — Universal healthcare with strong public reimbursement; supplementary mutuelle is common. The country with lower take-home often shifts costs that the other country leaves to your private budget.
Net-of-everything, a relocation decision should weigh basic public welfare in Switzerland against comprehensive welfare state in France, plus differences in pension capture, social safety nets, and city-level cost of living.