Speaking personally fellas, I don't know if Rommel would have stopped the invasion or not had he been allowed full use of the Panzer forces but the slaughter would have been horrific like all landing beaches most are not that big (Omaha beach was 7000 yards but a lot of that was not easy to negotiate) so it tends to funnel the fighting into smaller pockets to avoid strongly defended areas of contact, or areas with better cover for the invading forces rather than maintain extended lines. I dread to think what it would have been like with Panzer units holding the high ground looking down on the landing fields.
Sorry to back track a bit lads the Seargent I referred to was a time serving WW1 vet and he had a son in the paras when my old man went home on leave one time he met him in a pub and the old boy was in a terrible state it turned out his boy had been killed at Arnhem. He took the news really badl. He never did get over it and died a couple of years later.