It’s more about being trained than the weapon itself. Yes, a rifle is more effective than a pistol, but training is critical regardless of the weapon chosen. Not every teacher can or wants to be SEAL. And to be adept at non-lethal and lethal defense, active shooter, etc, takes significant time and skill. While having all teachers trained would be ideal, having ANYONE trained on site now is better than waiting for police who might not be trained for active shooter themselves.
Can’t disagree with anything you said.