In Occupied Economies (https://www.amazon.com/Occupied-Economi ... 1845208234) we have estimates of the GDP of 6 countries occupied by Germany during the war (including black market output which surged following German occupation), I also included figures from Klein (1957) of German GNP and weighted all these indexes in proportion to pre-war GDP using the PPP estimates by Willianson (1995):

Some economies declined while Germany experienced some moderate growth, overall there was a very small growth over the 7 countries' block by 1943 compared to 1938.
Compare now with the macroeconomic performance of Austria-Hungary, France and Germany in WW1 (The Economics of WW1 https://www.amazon.com/Economics-World- ... ics+of+ww1):

Which was characterized by almost total collapse. By 1918, Austria-Hungary was starving while Germany was on the edge of starvation:
Cereal production Germany
1913 --- 100
1914 --- 88
1915 --- 71
1916 --- 72
1917 --- 49
1918 --- 57
Still even in WW1 they managed to maintain the level of coal production at nearly 90% of the pre-war level as well as expanded metal-working industries, while in WW2 continental Europe's coal production actually increased a little bit from pre-war levels:

Sources:
WW1 - Race to the Front
WW2 - Jason Long's website The Sinews of War: Economics, Production, Logistics.
Real wages also declined further in WW1 versus WW2:
German real wages (source: The Economics of WW1):
1914 - 100
1915 - 88
1916 - 79
1917 - 65
1918 - 66
In WW2:
Real wages in 1943 versus 1938 (source: Occupied Economies):
Germany ----- 110
France -------- 58
Belgium ------- 95
Netherlands -- 77
Denmark ----- 86
So most of Europe under German occupation in WW2 was faring better, even in terms of real wages, than Germany was in WW1.
What was the reason? Well, both in WW1 and WW2, the economic collapse was caused mainly by massive conscription which deprived all the countries' economies from labor force (although the maritime blockade hurt significantly as well). In WW2, Germany conscripted millions of people from occupied countries to work in Germany, that was according to Occupied Economies, the most damaging policy the Nazis did in occupied Europe, although that helped to prevent Germany's economy from collapsing like it did in WW1.
Another reason for the discrepancy in GDP performance in WW1 versus WW2 was that in 1938 the world was in the Great Depression so output was already below potential, while in 1913, the world economy was almost at full employment.