To demonstrate competency in handling simulated EFATO, or any other emergency in the book, is not that complex or demanding. (It's not space-shuttle.) The dangerous , and in this case fatal, problem is not in any sense procedural . It lies in the embedded fraught issue of complicating the business of check and training with an underlay of unrealistic expectations. You have to consider the mindsets at work.
First impressions , what may have happened here, from reading the foregoing posts, is that there was a mix of competent but somehow distracted parties on board, not sharp enough at that time, on that day, in the prevailing circumstances, to foresee the hidden trap that was their undoing.
Whatever the final report comes up with, we may be sure that there will a significant element of conjecture. (Like the RAAF 707 off Sale, no one survived to add first-hand veracity to the conclusions.)