6 of 8 in my Delta interview class were hired.
One of the guys who wasn't hired had never heard of Emerald Coast and after a couple minutes of conversation I realized that he had no idea of what the SARR or STAR story format was. He was told that he failed the panel interview.
The other guy also failed the panel interview. When we asked him what he thought was the problem, he replied that he had a failed a few flights and had a rough time in UPT. Also, that really didn't want to talk about it with the interviewers. He mentioned that he was expecting them to ask him questions about himself. Not trying to twist the knife, but that is a terrible perspective to have during an interview. You have to be willing to talk openly about your weaknesses/failures. I was surprised to hear that he HAD done the EC prep because during my EC prep, AH made it very clear that it is ok to have hooked a few flights along the way and all they are looking for is that you recognized your weaknesses, learned from your mistakes and became better because of it.
Do the prep. It helped me tremendously.