"[...] bank accounts are taxed at a flat rate of 34.20 euros for each bank account where its average balance is higher than 5,000 euros.
Doesn't that mean that with bunq you actually have an advantage in comparison to other foreign accounts? Because you can have many accounts for no additional fees, then it should be easier to have less than 5000 Euros on each of them.
But it also seems like this 34,20 euro fee can be deducted from your other taxes that are due, not completely sure, just going off this website. So maybe that'd be a chance to get them back :)