Whenever I hear it at the range I shoot, I typically stop listening to the speaker right then and there because what usually follows is a 2 shot group...
I also hear, "This gun can't group worth a dang!". Again, it is typically shooter error, or the shooter hasn't tried a different type of ammo. From what I see, it is not usually the rifle that cannot shoot MOA, but the shooter.
I have found ammo that each of my rifles likes well enough to shoot MOA at 100 yards. My .223 AR 16" M4gery won't hold that out to 200 yards, but it stays close to 3" which is just fine for me. My new AR upper (18" match barrel) will hold MOA out to 300 yards (as far as I have pushed it). My .270 WSM will hold MOA out to 300 yards and my .308 shoots MOA out to 500 yards (haven't shot it further than that).
Even with that, I let someone shoot my .308 at 100 yards and they shot two groups of greater than 2.5" and were immediately bashing my rifle
