Everyone in this thread who was a working cop on the day of the North Hollywood shoot-out, please raise your hand. I was working a gang enforcement team at the time, partnered with street crimes guys & gang cops at a local PD. Three of them had come up from LAPD's West Bureau CRASH team - I'd met & rode with them when I went there for gang school. They knew the immediate ground pretty well.
Out in CA, pre-NHW/BofA, there were a few agencies that allowed or issued patrol rifles. We got our authorization in '93, after 5+ years of it going up and down the chain of command, because of an incident where a few of our deputies were pinned down on the hillside of a rancheria (small Indian reservation) for several hours while our SWAT team was a couple of counties away on a protest.
NHW/BofA absolutely drove the adoption of patrol rifles in Califonia. I can't speak for the rest of the country, though.
Could a 9mm carbine have ended the event? Maybe, maybe, though, it would have been an iron-sighted one. Maybe, the BadGuys were chemically altered. Maybe, the officer(s) would have had to deal with incoming centerfire rifle rounds. Maybe, the engagement distance was considerable.
Slugs? They could have caused some blunt trauma (backface deformation) to the homemade armor suits the BadGuys were wearing. That could have put them on the ground and allowed other options for finishing them.
One of the toolbags was hit by a pistol round while walking down the street & subsequently offed himself. The other one failed at carjacking another vehicle and then met three studs from D platoon - Anderson, Gomes, and a third officer. They engaged #2 under the patrol car from maybe car length and a half away with Mp5s, not quite the same ballistically as a PCC at 50 yards+.
Yes, carbines work more like your pistol than a pump shotgun does - but that's not why they took off after Feb '97. Remember, we weren't using optics then. The sight radius helped, as did the other marksmanship aspects related to a rifle - like 4 points of contact. The commonality of teaching stuff only came in years later. Hell, I recall a long conversation with @
paherne in the teens in which we kicked the commonality part around and that was a new concept to me.
BTW, as I recall, LAPD got the following approved in the aftermath: .45ACP pistols, slugs for units other than Metro & SIS, and
patrol rifles.
Personally, at a time when people are talking about cops needing to engage with long guns at distance - Uvalde? - the idea of a PCC is a hellacious step backwards. But, I'm not in that agency and I'm not dependant on them for support.