Rommels ghost and I will agree that the naval gunfire support and air support would have been devastating. Rommel, was aware of the overwhelming allied fire support from his time in DAK, that is why he advocated for the panzer divisions to be as close to the beaches as possible. Rommel knew and history has shown us that the panzers would be massacred while moving up from their assembly areas in the rear to reinforce the front.
However, when the boats are heading towards the beach you have to lift the bombardment to land them. Then you are left with DD's closing on the beach and direct firing with 5 inchers which would peel open a tank in 1 shot, but I doubt the accuracy would be very good.
So there are thousands of guys, soaking wet, seasick, no anti-tank guns, no tank support as the shermans were under 30 feet of water, carrying only the ammo on their backs fighting for their lives while being raked with MG fire from the heights and Panther tanks with grenadiers engaging them on the beach. Remember, that Omaha was almost evacuated, if panzers and infantry support had been available, there would have been no one remaining to evacuate.