I don't think it was so much that they were not prepared as they were under-prepared, which I'd say is a bit different, and even then that was more in terms of supply as tactically, they were very prepared. But in comparison to everyone else at the time, both supply-wise and tactically, they were very well-prepared I'd say. If they were ill-prepared, they'd have been throwing wild haymakers in the same way that the U.S., British, and Soviets were in the initial fights, but instead they very much knew what they were doing and they had the equipment to do it and were causing tremendous bloodshed. Their undoing was more in terms of being weak at the operational level of war and arrogance on the part of the military high command (the generals all blamed Hitler after the war but historians have found that is way overly-simplistic, Hitler was not the dunce he is made out to be). It took the U.S., U.K., and the Soviets some time to really get their act together and then it took an unimaginably high number of deaths (anywhere from 25-40 million on the Soviet side alone) and the combined efforts of the U.S., U.K., and the Soviets to defeat them. Keep in mind also that in the early parts of the war, from the perspective of the U.S., U.K., and Soviets, the Germans seem VERY prepared. It's only in hindsight that we know that wasn't the case. The militaries of both the U.S. and U.K. both thought the Soviet Union was kaput.
So I mean while there are a huge amount of ways that the Germans needed to be better prepared, I don't look at Germany under Hitler and see how it matches up with your original quote: