To try to make a comparison between ISIS and the WWII German army is hard to understand. ISIS is no German-like operation. Right till the end of the war the Germans were bleeding the Soviets strongly disproportionately. And they were doing so against a Soviet Army that was massivly better supplied (by the US) than the Germans were. The Germans went the entire war supplying their forces with horse transport. But when the Russians arrived in Berlin, they were a 100% motorized force, riding into the city in American supplied trucks.
The US and Britain did not take on the German army in central Europe until the Germans had been throughly bled by the actions of the Soviets, by a relentless bombing campaign and attacks around the periphery. Prior to D-day the US and Britain attacked in places where the Germans could not bring their superior tank forces fully to bear. Italy: We attacked up through Italy, some of the most defensible terrain in Europe. It was not for no reason that the Roman Empire arose on the Italian penninsula. We suffered disproportionate casualities in Italy because the terrain favored the defense, but at the same time it was not good tank country. So the Germans were not allowed to bring its undeniably superior tank forces to bear on a lightly experienced American army. The Germans were just that good, that we were not at that time able to fight them straight up.
North Africa: Both Britain and the US fought the German tank forces in North Africa. And it was there that we were learning to fight the Germans. Had the Germans been generously supplied in North Africa, its doubtful we would have had much success against them. But the Germans were fighting at a supply disadvantage in North Africa. The allies had control of the Mediterrain and the German tank forces struggled to get the supplies necessary to fight in that theater.
How the allies were so careful in the way the German tank forces were engaged is a testement to the quality of the German forces. We never took them on when they were fully supplied and with the German air power fully intact. The Germans were just that good.