It's still a silly, overexposed gun.
And the prototype is from the 70s, yeah, and eventually became the USAS-12. The current incarnation has very little in common with it, and it's the one that is OMG TEH BEST GUN EVAR, with only a dozen in existence...
Why game devs never seem to do with something we haven't seen before is utterly beyond me. Similar thoughts about the SCAR being in every modern shooter (lolhyperbole) since the first GRAW, despite the fact that there are only a few hundred made and they are used exclusively by a few ranger battalions.
And yeah, I know it's not futuristic or anything, but realism isn't really the concern so much as originality or imagination. Hell, if KF were realistic, Britain would be a lifeless wasteland considering that guns are sparse there (except those MAC-10s that pikeys seem to have no trouble getting their hands on, or the AR-18s that the IRA seems to love). Or they'd just say OMG THINK OF THE CHILDREN and ban zombies, making them disappear forever (sorry for stealing your joke balci).