I'm sure there is an SOP for dealing with flooding vehicles. The Marines weren't under a really threatening situation until the second track collided with them. That was human error on the part of the other track commander. The ranking man in the sinking track should have taken the initiative to have his men prepared, even prepositioned to exit.
Your argument This wasn't an "accident:" the incident was inevitable given the lax safety training and poor maintenance. assumes systemic problems in a case where it was, in fact, a unique situation, two tracks colliding.
I fail to see where that is "inevitable" considering the frequency of amphibious operations that occur without such incidents.
I read most of the accident report.