You make it sound as if Omaha was a cake walk. It, as I’m sure you know, was anything but. With all that firepower and those prepared positions you mentioned, the defenders did considerable damage. The first and second waves to arrive on the beach suffered extremely heavily casualties- especially on the eastern/western ends. I’ve seen it given as anywhere between 40-80%, for a total of approximately 2,000 killed, wounded and missing.

But it was a success, despite the heavy price. It was, in no small part, down to the effectiveness of officers (both junior and senior) in leading experienced troops. The main assault was comprised of the US 1st Infantry Division, and the 116th Regiment - detached from the 29th Division. Although the 116th was inexperienced, the 1st was a veteran division of North Africa and Sicily. In Sicily, they had taken part in Op. HUSKY and gained experience of opposed amphibious landings. Very, very little went as planned but despite the casualties, they were able to break through the beach defences at multiple points. Perhaps more impressive is that the green 116th was able to do the same, as small impromptu units organised themselves and fought their way inland.

However, the infantry weren’t alone. Despite the popular myth, there were tanks on the beach and these gave invaluable fire support in forcing exit points. At least one American officer, in the 116th, credits the armour with saving their situation. Equally, the navy did their part. Several destroyers closed in to, in cases, less than 1,000 yards and gave direct support. In one case, a immobilised tank was able to get the attention of destroyer and direct it’s fire to where it was required.

There’s also a case to say that a good number of the troops opposing the landing were Osttruppen. These were troops recruited from Eastern Europe - often Soviet POWs - and were of, frankly, questionable quality in some cases.

Tl;dr - the Americans had excellent leadership, some experience of that sort of thing and more support than people often think. Perhaps most crucially, they were able to improvise when necessary - in the face of all their plans going to shit.