Hitler had no understanding of the economic power of the Soviets. They outproduced the Germans many times over. In fact when Hitler realized how much the Soviets could and would produce he said to paraphrase “I would never have attacked them”.
By the time D-Day rolled around the war was already over (excluding some miracle weapon). WW 2 was really a battle between Germany and the Soviets. Had Hitler been able to knock out the Soviets quickly he would have won WW 2. Had he forced a Soviet collapse in 1941 which by the way he did have a real chance of doing WW2 would have ended then and there. The Germans would have been able to redeploy their forces against the Brits and wipr them out in Africa as well as the Middle East as well as join up with their Japanese allies. Had this happened the combined forces of the western allies would have no prayer of defeating the Axis. After Hitler attacked the Soviets (June 22, 1941) a minimum of 60% of German strength was devoted to fighting in the east. Had even half those forces been avaible to fight in the west it is obvious that at best the western allies could have hoped for was a truce to avoid outright defeat. As Hitler never wanted to fight the western allies this is probably have been the end of the war.