@Glennn,
First of all, the officers would not go in in Uvalde because of the weapon that was being used. This was a.command decision, not each individual offocer. We know of a few officers that wanted to go in but no command to go was given.
The AR15 can be turned into a automatic by simple engineering of the selector device. The mechanics are already there - the gas exhaust that rejects the used cartridge.
The bullet is also what makes the weapon a real bad ass. It is barely bigger that .22, except it starts rolling after being fired. This turns it into a .45. The bullet is also made to disintegrate, widening its area of damage. And, it has a lot, lot more propulsive power. More pop for the bang.
You are wrong in thinking police aren't worried about long guns in an exchange (fire fight). A machine gun would take it to the next level! When they enter a situation - they want to know where the long guns are, especially military grade weapons.
I assume you are a "good" person. I have no problem with weapons in the hands of good guys. Since we can't control who gets the guns, I would prefer no civilians get automatic or semiautomatic military style long guns.