Well, it is true that it is used lesser and lesser in contemporary spoken and even written German, but you need to learn it anyways , in order to be able to read and understand older texts for example and still many times official documents and articles. It is a beautiful form , that sounds a bit complicated for newer generations ,who are dealing mostly with the internet language ,that is shortened and abbreviated. It is much easier to use Dative instead . The commentator is correct though in his observation. Using the Genetive is declining specially in the spoken language , yet it has to be learned and preserved as the original language !