Their old assault rifles were broken and or in need of repair. These are virtually free replacements. No issue here. If it were something other than standard high powered rifles, that I feel the cops must have access to, I might question it, but not this time.

No argument here about the PD's need for accurate firepower, even considering its limited application. What does need to be questioned is their use of the AR15 in place of the previously used shotgun for close range protection. It's easy to miss a target in times of stress, and the .223 bullet will travel a LONG way before it finds something else to hit. Shotgun pellets not so far, and they're more likely to hit the target in the first place.
But not to worry, the MVPD always operates its equipment flawlessly. Except for occasionally running down a bicyclist...

Someone needs to look up the spread of shotgun pellets....there is more than one kind. And how do you know they weren't using slugs?