He's a grieving father, so we have to give him a brak. But, if what he is saying is correct, he's right.
The last training I conducted as an SRO, we practiced our response to an active shooter scenario at a local school. During the summer, no kids around. We practiced this type of scenario several times.
You go in, one at a time. There is no waiting for backup, no waiting for proper equipment. As our instructor put it: "You go in. You have plenty of training, a gun, a radio and a set of balls. You go in and stop the shooter."
If necessary, you step across wounded deputies or other victims. Your sole focus is to close with and eliminate the threat. Once the threat is neutralized, there will be lots of holp to render first aid and evacuee the wounded.
If the Uvalde Police Department waited, they were doing it wrong.