Good points. Also to be included was Hitler's refusal to move troops from Calais until it was too late.

Rommel had been building up the Atlantic Wall since he took command of it at the beginning of 1944, but there were ammunition shortages that he hadn't fixed by D-Day. The bombing campaign on top of the Germans fighting on two other fronts were factors in that shortage. As far as I know, however, the Allies won the battle by sheer overwhelming numbers before the Germans ran out of ammo.