I don't know if those officers who were relieved of their duties deserved this or not, but I can't help but think that there was a lot of outrage against the loss of life on the AAV that was behind the investigation and that may have led to the actions against the higher-ups.
But these men didn't die because of a decision somewhere to look the other way on a report or on a training matter; they died because of piss-poor decision-making on the AAV at the time.
The incident took place over thirty minutes. At what time does an NCO give the order to have everyone drop their gear in the troop compartment and get topside with their life vests? If it wasn't when the water was up to their ankles, or even up to their knees, when was it?
Forget about what some colonel did or didn't do. Who was in charge on that boat?
But it also seems clear that the NCO did not receive proper training (nor did the men in the AAV), and that most of the AAVs in the exercise should never have been used.
Both the training and the maintenance were the responsibility of the higher officers.
No one in the services seem to have any interest in addressing these root causes, probably because close examination would show that officers from lieutenants to four star generals have been lying consistently about readiness for years. They'll hang these two out to dry to distract from that.