5% may not seem much for Germany. That's roughly 4 Million people. But then again that's almost the population of Norway. And as Norway proves, you can certainly do very well in winter sports with this amount of people if things are well organized on that front.Regarding Germany as a winter sport nation: When only 5% of the country have snow in the winter winter sports get a bit ridiculous.
However, Germany can't really complain about struggling in winter sports in general. They are usually among top 3 countries in winter olympics. It's just that their focus of attention is more on several other winter sports than XC.
About Tour de Ski the only thing I would mention is that with the absence of Norway I would have expected Sweden's team depth to really shine through in women's side. But that's not happening, at all. Ebba Andersson is almost shockingly poor. I guess while everybody else has been in central Europe and in altitude for weeks, Sweden and Finland are really struggling having arrived there late after having skipped previous world cup races.