But the two fronts were by no means proportional - throughout the war the overwhelming majority of the German Army was engaged in the East.
I never claimed the two fronts were "proportional". You made the assertion that "US prioritizing the European theater did little to effect the eventual outcome", and I merely pointed out that this is entirely incorrect. Clearly the US had more than a little effect on the German war effort. As your own stats show, the western allies tied down massive numbers of German divisions.
You can see here (http://www.axishistory.com/index.php?id=7288) that the number of German divisions deployed in the West did not change significantly after the US entry into the war in early 42
Those are fascinating numbers, but they really do prove my point. Germany started with 145 divisions committed to the Eastern front at the start of the Russian invasion. This number grew steadily until it peaked in Feb 1943 at 195. From here on Germany was steadily removing divisions from the Eastern front to deal with the growing western threat. In Dec of 1941 Germany had a total of 45 divisions dedicated to the west, Africa, and Italy. Evidently Hitler gambled that US ground forces wouldn't be an immediate threat because he drew this total down to 30 divisions by June of 1942. From here however the number only increased, with obvious spikes concurrent with Patton's landing in Africa in the winter of 1942, the invasion of Italy, and Normandy.
Normandy had little to do with the success of Bagration (which dwarfed Normandy in size and Axis casualties).
I have no data on casualties, but it is interesting to see that in May of 1944 (the month before Op Bagration and Normandy) Germany had 160 divisions on the Eastern front. By July Hitler had pulled 36 more divisions from the Eastern front,
despite the huge offensive by the Soviets. Obviously Hitler viewed Normandy as something other than irrelevant. Also, Germany's huge problems of long supply lines and fighting an army intent on defending it's homeland slowly turned around as the Soviets pushed the Germans back. Now it was Russia's turn to face these obstacles. Without a second front, it is extremely likely that the Russian advance would have turned into a protracted stalemate much like Hitler ran into in Stalingrad. The fact that Russia was able to push the Germans back at an accelerated pace in the second half of 1944 just when they faced their longest supply lines and the most determined German resistance proves how critical the second front was.