As for the video of the shooting in Lubbock Texas... the man with the gun did everything WRONG! As a responsible gun owner I have to publicly go on record and distance myself from people like that. Castle Doctrine or not, folks that are eager to kill other folks aren't quite right in the head. That situation is a lesson in why not to bring a firearm into a verbal family squabble.
As for the weapon used... at the 7 to 8 feet distance the muzzle was from the target, a Davis derringer loaded with the same round would likely have terminal effect with the same shot placement.
^^^ All that being said, sure I think a 9mm carbine is a very effective weapon for law enforcement and legitimate SD/HD, especially when paired with a pistol that accepts the same magazines. I'm a big Ruger fan, but I don't own any Ruger semi-auto pistols. Not a big Glock fan, but they’re ok.
I've been a fan of S&W 3rd generation semi-auto pistols for 3 decades. So unless an adapter comes out that would allow me to use the PCC9 with my S&W 5900 series magazines I'd just as well have a vintage Marlin Camp-9. Same concept; different look and feel.
Back in the day I had the opportunity to handle a few different 9mm carbines when they were becoming a thing; the original Ruger PC9, the Feather Industries AT-9, and the Marlin Camp-9, at Don's Guns in Indianapolis. An Illinois State Trooper friend and I took a day trip to check them out. A good time was had by all.
the Ruger was nice, but I decided the Marlin Camp-9 would be most suitable back then, but never got around to buying one. (so many guns, so little time and money in those days). I liked the Marlin not only because of magazine compatibility with my S&W pistol, but also for the look and feel over the others.
All of the 9mm carbines available then and now give the user some advantages over a sidearm. In addition to a little more pep in fps, greater sight radius and stability for longer shots are among the benefits.
I still use Federal's 9BPLE +P load (in those days along with the 115gr W-W 115 +P+ AKA Illinois State Police Load) and Corbon's original 115gr +P. Corbon is 1350 fps from a 4" barrel. That round has been clocked at 1600+ fps from a 16" barrel carbine. Pretty zippy. Well, I've got the pistol and plenty of extra mags. All I need is a Camp-9. I hope to add one to my collection, lightly used, one of these days.
Can't get over that video. All I can say is if a guy is not at least as good with verbal judo or some form of de-escalation skills as he is at using firearms, he's not ready.