If the Grendel cant get it done past 200 yards it is a product of the shooter not the cartridge.
Thats actually an intelligent question.
The answer is both and more of course. Real hunting shots are a compromise, i.e. not as perfect as shooting at paper from a bench. Bullet placement is often "off" a little from ideal because (a) the animal doesnt cooperate and (b) the hunter can't break the shot nicely. I'm going give a wild-ass guess that 80% of hunting shots are the "compromise".
Empirically, we know that increasing the impact velocity of a bullet increases the damage it does to the animal. And when the velocity exceeds a certain threshold, the damage is more than just the frontal area of the bullet crushing tissue. This isn't news, we've been using this since 1925 when the 270 Winchester was introduced.
But today folks are trying to wring all they can from "wimp" cartridges - cartridges limited by AR-15 design constraints. And these cartridges aren't even 30-30 power level at the muzzle. So these cartridges don't provide much "extra" to help make a quick kill with the "compromise" shots. Any margin the Grendel had is pretty much gone much past 200 yards, and "compromise" can mean lost animals. OTH, the 270 Winchester for example, will still turn a deer to mush at 200 yards - offering much more margin for those "compromise" shots.
Yes there are stories of an Inuit grandma taking a polar bear with a 22lr. But the are a lot more stories of Inuit's encased in bear scat. "Use the right tool" - Anton Chigurh from 'No Country for Old Men'.
