It is not a systemic failure. It is a human failure. The best laid plans of mice and men often go awry. It is the same fallacy the liberals use when they think they can solve problems with legislation outlawing guns or other kinds of behavior. Just because you have plans and procedures don't mean that they will be executed as written. The human element is not always under control. As von Moltke said, "no plan of operations extends with any certainty beyond the first contact with the main hostile force."
When you dont change your oil in your car and your engine fails it doesnt matter if a crankshaft or a piston shattered it means the entire system as a car is now broken because it cannot move forward. That is systemic failure.
The car can be running with perfect efficiency, but an incompetent driver can run it into a ditch and render it inoperable. The four deputies that hid outside the school did not follow proper procedures. Peterson was suspended without pay for dereliction of duty. Who knows how many lives and injuries could have been avoided if someone other than this coward had been at the school?