The most recent proposal for the Netherlands is a 1.75% tax on your invested net worth on January 1st of the year. Even when the market went -10% in the year before. But even at the market average of 5% per year that is a big hit. If your average Joe puts €200 a month in index funds for 40 years, the end sum is €304,000 without wealth tax or €198,000 with wealth tax. That is a big difference on the type of additional pension a person can build. We have tax deferred accounts but those have very low limits for the average earner.
But the upper class don't care about it. They have the means to put their money in a shelter or company and let it grow against a much lower tax rate.
* €200 a month, 5% market average and 1.75% wealth tax