It was not.
Quite simply, German economy roared from 1948 until the mid-1970's for a couple of reasons. First of all, there was almost no war debt. The Great War debt was reduced to a half at the London Conference in 1953. The WWII debt was rather minuscule. The Western Allies knew they would need a new strong ally against Stalin pretty soon. That's why they were so generous.
Another thing, which allowed German economy to flourish, was relatively low tax burden. As it appears, tax collection to GNP ratio was smallish by the present day standards.
Few countries have such a light tax burden now: South Korea comes to mind. It's in the middle of the economic miracle of its own. Hardly just by chance.