The 6.8 was designed to increase lethality in an M4 pattern rifle over M855 from 0 to 500 meters for SOCOM
if that was the case then someone definitely didn't try to think inside the box very well. M193 ball would increase lethality over M855 penetrator rounds quite easily.
to say that it was designed to increase lethality over 5.56x45mm would be a more politically correct statement.
6.8 is a medium weight carbine round designed with semi autos in mind, the 270 can do everything that the 6.8 can and more. the 270 just can't fit inside an AR15 receiver which is what led to the 6.8 development.