By D-Day the Atlantic Wall defenses had been reinforced several times, even taking seriously the need to muster and build up stockpiles in Britain an attack could have broken through the coastal defenses earlier.

…but those defenses were still enough to force a concentration of forces into a single spearpoint, which inland reserves could have mobilized to encircle and neutralize.“… until they were redeployed to the Eastern Front. It really was Russians fighting in the east that decided the European theater of WWII.

Of course, Stalin exerted whatever pressure he could to bring the West into the fight ASAP, but letting the Red Army bear the burden and pay the costs of attritting the Reich away and then only afterwards sweeping through a hollowed-out Western Front as the preferable option to surrender to was a critical part of Anglo-American grand strategy.

Even with that, they still then had to grind out a Cold War evenly matched enough to last half a century.