> Unless you live in a temperate climate heat pumps have to be really oversized (3x? If it gets really cold) to work in winter.

I think people are stuck in the past when it comes to heat pumps honestly. People install even air based heat pumps up here in northern Sweden.

Yes, if it gets extremely cold you will probably be using some direct electric heating as well. But how often does it get to -15C in the Netherlands? The level where good modern heatpumps really start to struggle. For a typical Dutch winter heat pumps should be no problem what so ever from a tech standpoint.