I'm weird when it comes to aesthetics and how some guns are "supposed to be"
To me, a carbine is supposed to have a 14.5" barrel. If I can't have that then I see no reason to half-ass it. May as well just get a full-length 20" rifle.
It's not just aesthetics though.... The carbine length gas system is designed for (roughly) 10-14.5'' barrels. When you start using it on longer barrels it tends to put more force on the bolt/lugs and can
(not always, I know...) cause sheering. From my understanding, this is why Colt now puts "H" buffers in their civilian 6920s. With the exception of my Colts, all my 16'' ARs are middys for this reason. Just throwing that out there