Non-standard AR-15 components and magazines are a turn-off for me personally just like it is for my Six8 rifle.I disagree. The grendel outperforms the 308 past 500 y and is a great hunting round for varmints and deer. Plenty of bullet options and easy to handload for. Not to mention it does well in a SBR platform.
Shooting a deer or varmints at over 500 yards never really crosses my mind and I live in Texas! Pronghorns and Mountain Goats and the Grendel aren't a good mix for me either.
Small groups at long range (>600 yards) is what I generally think of but, my 10.5" up close works well and high sectional density long range bullets are good for special purpose shots.
If I am hunting over 500 yards, I'm going to start with a 7 Magnum personally. If I wear out my 300WM, it will be rebarreled it to a 7 magnum with no regrets. Generally, I prefer larger bores so, call me biased as I rebarreled my rifle to 338-06 over other '06 options.