Having spent a fair bit of time contemplating the merits of the Grendel, and writing about it in this and other fora as well as on my own website, I am reasonably sure that arguing the military merits of this cartridge is a fun sport. Problem is that political and, perhaps, a few technical & logistics arguments make the sport more like that of debating on how many angels can dance on the head of a pin. We get insight from the exercise that may be useful for this and other discussions, some of which may actually pan out in the form of production hardware.
Mehavy's trajectory plots are very useful and make the strong argument that there is not enough difference in performance between the Grendel and other cartridges optimized for deer-hunting to make a difference under 250 yards. The animal is as dead either way, adequate blood trails can be expected, and the crosshairs center in the vital zone will generally make the hit absent shooter error or bizarre conditions. The 30-30 with proper bullets and zero, 257 Roberts, .243 Winchester, the .308 Winchester, the 6.8 SPC and a bunch of other cartridges have this characteristic. The Grendel and the SPC stand out because they are cartridges designed to operate on the AR15 platform.
The thing that differentiates the Grendel from the SPC for hunting and target shooting is that it does indeed have the reach to be effective over the longer ranges for both hunting and target shooting. In fact the Grendel is reported to be very effective in target shooting at the 600 yard range.