For the sake of argument (and simplicity) let's say that schooling and other childhood / early adult expenses for the average citizen cost the state $100,000, and let's say that in return the state is likely to gain $200,000 in tax money back from citizens over their lifetime once they become productive members of society.
It's pretty obvious that if you give adult immigrants who can immediately become contributing members of the economy a 1/3 tax discount that the state loses nothing, and only stands to gain from the deal, since they never had to pay those $100,000 to send them to school as children, that cost was offloaded to some other nation-state.
The tax contribution of those immigrants to social programs like welfare is also going to be just the same as the contributions of native citizens, despite the lower tax rate, because the state isn't also using that tax money to pay for those $100,000 it never spent.
If anything the flaw in the Dutch policy is that the tax discount isn't large enough, should last for more than 10 years (i.e. indefinitely, and should be larger if you promise to get out of the country before retirement), and that they should offer it to more immigrants, not just the highly skilled.
The welfare state has a limitation: it needs to be paid for. It also has a consequence: people who seek welfare may attempt to move to the welfare state in order to obtain it. This may imperil the ability of the state to pay for the welfare - or, at least, the willingness of the taxpayers to fund that welfare.
So this impacts immigration policy. Insofar as the welfare state IS like an insurance policy, this is like the health insurance company denying coverage for a pre-existing condition.
