I think is true for single detached housing, is it also true for larger apartment complexes? I bring this up because in Germany I believe most of the population does not live in detached housing or semi-detached housing.

With larger apartment complexes it may be economically feasible to pursue geothermal heat. In this case a more efficient solution could be a heating arrangement using hydronic heating combining geothermal heat, waste heat, topped off with an efficient large-scale boiler (the apartments need hot water anyway), and then pumped into radiators or underfloor heating.

And naturally the most efficient solution of all could be district heating.