I'd love to know the source; the author is making a bold and incorrect statement.

Manstein, Kesselring, Model and Hausser (who was perhaps promoted past his abilities) all showed incredible defensive skill.

Further, the German defensive doctrine was almost continuously built along an 'elastic', flexible doctrine; playing to the German's strengths: attack. Trading space for time, rapid counterattacks by all-arms 'fire brigades' and separate but mutually supported strong points all feature in the tactical and strategic defensive doctrine of the German army, all of these principles tried and tested in WWI.

These generals embodied these doctrines and prolonged the war and kept lines relatively stable despite rapidly evaporating cohesion in the Army organization. I'd say that's a defensive accomplishment and a sign of keen minds.

I would say your premis is wrong. Albert Kesselring for example made a brilitant devence in italy.

Also depening on how you interpret defensive, then some of the counter offencives from von Manstein where up there. In fact the the german army overall, collectivly defended very well, almost in all battles taking more from the USSR then the other way around.