There are a few issues..was there an order in place that was broken? "Only vehicles equipped with armor and anti-bomb widgets will be used outside the secure area"--if such an order was in place and that order was violated, then someone is in violation and should be charged.
Or, if someone lied and did not represent the situation on the ground correctly --"We are perfectly safe in unarmoured vehicles and don't need to take extra precautions" then that person would be guilty of dereliction of duty.
What is achieved is accountability--if in fact there is something to be accountable for. But as you state "that is the responsibility of those sending the troops to war not the officer on the ground", I believe that sending people into harm's way ill equipped should be something to which someone is held accountable--but in our system of government that person is not a military officer it is the SECDEF.
Unfortunely, those level of people seem to be beyond reproach and it is kids like Fusilier Gentle, and some junior officer that gave the order that pay the price.