This loss concept is just a myth: the new tax rate only applies to the amount above X. If you're at the edge of the 45% rate, the extra 100€ will be taxed at 5

This loss concept is just a myth: the new tax rate only applies to the amount above X. If you're at the edge of the 45% rate, the extra 100€ will be taxed at 50%, but the amount you earned previously will not be impacted and still be taxed as before.