> on realised employment income is more progressive

Most of income from employment is "unrealised". Employment comes with expenses such as car for commuting, rent in expensive part of town (where jobs are), clothes... Big part of "income" does not even land on a bank account (mandatory insurances, taxes, child support, alimony....)

If we will apply logic from property tax, to employment income tax, everyone would pay 100 USD tax every year. Because that was tax of 20 years old in their first job, and raising taxes is horrible!