I think 9mm carbines are great.
The Luger carbine was a great weapon IMO.
The HK94SG1 was a superb weapon, claw lock scope mount, factory zeroed Leupold 6X scope, HK93A2 stock with adjustable cheekpiece, Harris bipod and flash suppressor - out to 90 meters it was as accurate as any rifle.
But the shotgun does some things better and the 5.56 does other things better... I wouldn't choose a 45 or 9mm carbine in a break in - I'd choose a shotgun. And if I had some weird situation where I had to engage enemies past 25 yards, I wouldn't chose a 45 or 9mm carbine, I'd choose a rifle.