the netherlands should raise the threshold to 5%
No it should not, as the current threshold ensures a variety of representation in a deeply pillarised society.
Hasn't been like that for a couple decades now, which is exactly the problem. In the era of pillarization, you could have a dozen parties in parliament and the system would still handle it because every party's support was stable and everyone knew what to expect.
Anyway, 5% wouldn't solve anything. The problem isn't small parties getting in with 0.x% of the vote; it's the overabundance of mid-sized parties that have no other option but to govern with the sole major party; but that party, unlike the old CDA, isn't centrist and you end up with ideologically incoherent coalitions and compromises that make all sides dissatisfied.