That would be a long story to debate. However, I think you can't use US/Nato definition to set standard on Soviet/Russian weapons just as you can't use WW2's definition to set standard on today's weapon.
The carbine definition predates NATO. Second the term SKS is an Acronym for.... Samozaryadny Karabin sistemy Simonova or Self-loading Carbine of Simonov. And that’s with a 20 inch barrel. SKS was a carbine when compared to the 29 inch barrel of the Mosin Nagant. SKS was being designed as the Germans were being pushed back to Berlin (44) and The AK was designed in the aftermath having been inspired by the StG who’s early form was designated Maschinenkarabiner 1942. German being close enough to English the term Machine Carbine 1942 shows through.
So I am using the proper definition not just from NATO but the Russians themselves and the World war 2 definition fits as they were designed in that era. AK was a carbine same as StG was they both got called Sub machine gun (MP) but that was as the terminology wasn’t clarified yet.
the traditional definition of a carbine was a short rifle or musket used by cavalry.
All modern infantry forces are motorized to some degree, in the old parlance Mounted infantry. Mounted infantry were a class of Cavalry. The Rifles we build for modern infantry were designed for mounted infantry. Or if you wish we could wait for the literal Horse cavalry units of the PLA to get the new weapons. But I think my case is pretty substantial as is.
