There have been vastly and disproportionately more where either the "good guy" wasn't any damn good and buckled in cowardice, or wasn't any good and accidentally shot an innocent, or wasn't any good and didn't do a damn thing but distract law enforcement when they got on scene.
It's pure and utter delusion to think that the truly rare instances of a "good guy" legitimately being any damn good and legitimately having any training to deal with an active shooter situation and legitimately having the stones to do anything are in any way indicative of a larger opportunity. They are by far the exception, and a vanishing small one.