The recent FSU case was an anomaly. The delusional/insane shooter had only a .380 pistol, and he hung around the front of the library as if he was literally waiting for the cops to come and shoot him.
That’s why the got there in about 2 to 5 minutes and shot him. (I have heard various reports on the time lapse.)
If he had had a pair of 9mm pistols and had gone deep into the library and up to a top floor and cornered 100 or more students, it would have been a bloodbath, and the cops arriving at the front door in just minutes would not have prevented it.
Only an armed student or staff on that floor with the shooter could have stopped it then.
If other shootings are any guide, the police would have stayed outside the building until they thought they had better control of the situation. That is how so many people died at Virginia Tech, the police didn’t want to take a chance that they might get shot. Also Columbine.