Jim and Kevin both nailed it. Jim on the firearm capability and Kevin on the YOU factor. Even if the firearm is a .3 MOA @ 100yds., in the real world past a few hundred yards, environmentals affect POI more than anything.
If the firearm shoots to a POA consistently at incremental distances AND you are "on" the environmentals(zero environment vs current environment, wind, density altitude,etc.) groups are smaller.