True, they did not lose the will to win as they were simply defeated by an organized force. I believe the Germans were involved in more than just fighting underground resistance in multiple countries. Such resistance alone did not defeat the Germans, but did assist with the final outcome.

Tito's partisans drove out their occupiers without outside assistance.

Now, Germany was obviously occupied on multiple fronts.

While I can't contest that if a nation of 330 million were to devote its full human and industrial capacity for the purpose of destroying all resistance in a nation of 33 million, it would succeed...

I wouldn't call the richest country in the world failing to convert to a war economy to overcome an enemy ten times smaller then they are to be 'lack of will to win.'

Yes, drove them out but did not defeat them in context of the war.

The richest nation in the world should not have to convert to a war economy to defeat an enemy ten times smaller. If it could not; then it didn't want to be there in the first place, it didn't want to do what was necessary to win, or their internal politics is screwed up. Possibly more than one of those.