The mistake many make: building a third floor in addition because the slope makes it necessary. Why not just two floors and the house with a residential basement as a full floor plus a second full floor, so one side as a bungalow, the other as a two-story house (simply put).
Well, the slope does not make it necessary, it is rather an option. With 1.5 floors, the area requirement increases with the same living space. That leaves little garden/terrace.
But the slope is not enough for a whole floor; upwards you are limited.
And of course, the requirements are not comparable to those of earlier times. And certainly the average apartment is smaller. However, the average represents a cross-section of the population in which a large part are singles without children and retirees living in big cities.
But yes, it can certainly be smaller, and the basement will also be reconsidered once the designs are ready.