Suppressed .300blk just punches clean little holes quietly, much like suppressed 9mm does. But it has 2 distinct advantages over 9mm;...1) it does that a bit further and a bit more accurately, and...2) it does so in an envelope that allows you to switch over to much more terminally effective ammo that essentially duplicates 7.62x39 by simply changing over to mags with supersonic ammo. And as a bonus,...3) allows you to do that with a weapon that measures no longer (with suppressor mounted) than a standard length AK.
No other cartridge offers all that together.