Although your account of the WW2 defeat is somewhat valid, and that I am sure Roosevelt and Churchill were happy that the Germans were happy to see the Germans heavily occupied on their eastern front, there are several points that need to be revised or included.
1. That for D Day to be successful only 2.5 years after the Americans entered the war is amazing in itself.
2. The logistical task for (1) was immense and geographically challenging.
3. The British were occupied in N. Africa or regrouping at home and the Americans were initially rather busy with the Japanese in the Pacific!!
4. But still by 1943 the Allies had commenced the invasion of Italy - enough of a distraction for the Germans to be considered as a second front.
5. The Battle of the Atlantic was not won until 1943. Before that it was too dangerous to transport large quantities of men and materiel to Britain.
6. Several months of training was required for the allied forces in preparation for D-Day, which was not feasible through the winter months 1943/4.
7. Extra time and resources were required during preparation to try to foil the increased number of German spies in the UK.
8. The allies had to wait for good weather (summer months of 1944) to avoid a completely wasteful disaster.
9. By May 1944 the Germans had 58 divisions in northern France, not 10 as you claim.
10. Many of the poor buggers at the German eastern front were killed by freezing cold and hunger - not bullets - and this was Hitler's biggest cock-up.