There were more then a few points you seem to have missed.
First off we knew it had to be a fast attack. Get in and on the ground. Secure the beach. Germany would could and eventually did bring massive amounts of power against us.
There were millions involved in the invasion. Most untested. To expect those who had never been under fire to react with skill and daring is absolutely ludicrous.
We could not advertise in anyway our intentions. So even the beaches and objectives were kept to last minute.
It is easy to plan, easy to sit back and armchair quarterback. To actually put together such a force. Keeping objectives under wraps at the last minute. Working with essentially green troops. Keeping everything secret. Weather forecasting not being reliable. Weather playing a large part in the timing of the operation. Trying to take as much area as possible as quickly as possible. Against an area heavily defended and able to call up more tanks, troops as quickly as they could. The operation was a resounding success. They did not have guided munitions, body armor, cruise missiles or any of our more modern war equipment.
WWII was over when we landed on D-Day. Germany knew it, we knew it, the Italians knew it and so did everybody else.
Germany wasn't fighting to win by that time. They had absolutely no (ZERO) chance of that happening. None. And I mean NONE.
Germany was fighting to get better surrender terms from the Allies. The Generals knew the War was over in mid-1943. So did everybody else. Except the socialist Hitler.
The German fighting machine was good, but they weren't as good many think they were and, most importantly, they weren't as good as THEY thought they were. We (The USA) basically bitch-slapped them from one end of Europe to the other.
They were very over-rated. Bigly.
Their tanks weren't nearly as good as myths have them, their fighters weren't all that great (at all), they had no Heavy Bombers, their Navy was sunk before we even entered the war and they spent too much time and energy on bullshit projects that did them no good. The King Tiger was a complete waste of time. It spent far more time broke down than it did running. It was actually a liability in the field. Even the Panther was way, way over-rated. Big time.
The MG 42 was the absolute best Machine Gun of the War but the Mauser '98 was a dinosaur. A good weapon in WWI but in WWII, almost useless.
Some of the best weapons, believe it or not, were fielded by the Russians. The T-34 was the best tank (BY FAR) of the War.
It had a diesel engine (no, the Germans did NOT. A Myth) a 76.2mm Gun that would rock your world and a wonderful suspension. Nobody else even came close. It had a German engine, a British gun and an American suspension. And sloping armor.
So much of WWII is based in myths and legends. The truth is harder to find.
The average German soldier was well-trained, highly motivated and extremely well led. But they just didn't have the equipment like we did.
We were far more mechanized than they were. If you look at old pictures, you can see the Germans using horses in the field for artillery pieces, troop transports, ambulances, etc. We didn't. We didn't have to. German engineering is also highly over-rated. Our engineers were better in every aspect of the War. Still are. The Germans have excellent engineering but they have an ingrained tendency to over-engineer and over-build almost everything. Which wastes time and resources.
They never had a chance against us. It was almost laughable if it hadn't been so horrible