It's been the basic thesis of some 6.5G enthusiasts to beat the drum that their
chosen On-Bullet-To-Rule-Them All can replace the .308.
It does not
replace the 308Win/7.62NATO for what the cartridge can do
...and that it not what Grendel aficionados espouse.
What they do suggest is that if some cartridge is to replace the 5.56
-- and have as many of the ballistic advantages of the 308 as possible
while still maintaining the dogface hump/logistical advantages of the
AR/M-x platform -- then the Grendel fills that bill.