For this admittedly older OECD page:
Inequality of disposable income in the Netherlands is relatively low from international perspective, with a Gini coefficient of 0.28 in 2013, compared with 0.32for the OECD average. Income inequality increased between the mid-1980s and mid-1990s but declined thereafter, also during the years of the recent crisis. The ratio of the income of the top 10% to that of the bottom 10% is also moderate,with a ratio of 6.6, compared with 9.6 on average across OECD countries.
At the same time, inequality is high in the Netherlands when measured in terms of household wealth (property value, savings, private pensions): the top 1% of the distribution owns around 24% of all net wealth and the top 10% owns 60% of all net wealth, while the bottom three quintiles own almost no wealth. The difference in net wealth between the top 5% and the median household, as a share of median wealth, is 44 compared with an OECD average of 20
Perhaps the answer is that there are a lot ways to measure wealth. Assets and disposable income can be very different. Actual personal spending would be another - but that wouldn't include the benefits of intangible public services.