These are local policies. I'm certain (but have no time to look for the article now) that the Sheriff stated when suspending Peterson that policy was to immediately confront the shooter. Which he didn't. If you read the article you'll see that the Coral Springs police, different department and policies, entered the building. Joined by a Sunrise policeman, and two newly arrived Broward deputies. While others sheltered outside. My personal opinion, I think the sheriff lied about policy. The school deputy and the first arriving on the scene sheltered, that doesn't sound like a confront the shooter policy. And these policies aren't formulated to save the victims. Kudus to Coral Springs. I'll also note that as to an escape proof perimeter, Broward failed. Not criticizing the LEO in your family or his departments policies, thought I might disagree in many circumstances. But I think the Broward people are lying through their teeth.
Related, I realize police aren't military, but what happened to initiative. Is their no room for that in many departments policies.
What you posted is my understanding of the situation. The Coral Springs police (+one from Sunrise) had the guts to enter and confront the killer. But I also understand that by the time they all entered the shooter had stopped and was escaping by blending in with fleeing students. The shooting was very brief. 3-5 minutes.
The killer then whiled away an hour at Walmart, ate at a fast food joint, then was found and arrested. He probably could have killed more students but for some reason decided to ditch his weapons, ammo etc and escape the mayhem along with the students rushing away from the scene.