The coverage in Germany is really bad outside of the cities, area between Kassel and Fulda, and then further to the south is just a black hole. But when you enter into Austria on a train, you can say this just by seeing how fast internet is in the train, and there is a strong mobile signal...
In preparation of a demo, i spotted one last bug in our system, which i tried to squash together with a few programmers from the manufacturer, being online in Skype and Teamviewer basically the moment i sat down in Augsburg and managed to work around it when i had to exit the train 6 hours later.
This was around 2016, and at least on this ride there weren't much areas without reception.
Not denying the base problem though, once you get used to LTE you'll begin to notice if you ever drop back to 3G, or god forbid, Edge...