As I understand the reason why taking the beaches was so bloody was because no armor made it ashore, and that happened because the heavy waves made landing armor on the beaches extremely difficult. The delayed it at first over concerns of the weather so why not do it again? Was Hitler almost about to uncover exactly where they were going to land or something like that?
I'm afraid you're starting from a few false premises.
First, addressing your question of delay, u/KroipyBill explains that further delay would have made the invasion impossible; it was 6 June or nothing.
Second, it appears that you're working off a flawed understanding of the landings, especially as regards the tanks that made it ashore. u/the_howling_cow examines casualty numbers from the beaches here, and also includes a table of the tank units that landed. I also commend to your attention another post of theirs examining Utah Beach, which has not received as much media attention as Omaha. u/rocketsocks also here examines the landings as a whole.