Examining cause is important, but I was focused on solutions:
For example, lets say an entanglement occurs. The "cause" would typically be considered "entanglement," not OOA. However, if the diver also had a 19cu with them, they would have had enough air to solve the entanglement and surface. If a diver gets spooked, panics, and rockets to the surface, that would not be considered OOA. However, that same diver may not have panicked or taken a more measured approach if they knew they also had an extra 19cu emergency-supply with them. What about lost mask, dove too deep, got lost in a wreck, or .... many other "causes?" Setting aside medical issues, the addition of a pony bottle at least increases the fighting-chance a diver has.
Back to the "entanglement" example, I might also suggest a better (or even redundant) cutting device. Though even that has limits, for example, I sometimes come across thick steel cable underwater, which even 12-inch tin-snips wouldn't cut through. However, the "pony bottle mindset" often leads to divers considering better or redundant cutting devices, or various other solutions to dive-safety issues.
If a diver dies of a heart-attack underwater, sure the pony won't help them, but neither will gas-planning, skills, or anything else you talked about. Staying focused on the things a diver can control, redundant air is a fantastic, quick, and effective way of increasing safety (when used properly). And sure, people should also focus on skills, safety precautions, dive planning, etc as well.
