I'm not aware of another platform outside the AR that provides autofeeding an intermediate+ size round with the kind of accuracy and flexibility of the AR and at the price point that the AR hits that's readily available to civilians.
You can have an AR that's anything from a home-defense carbine tricked out with all the tactical gear to an AR set up for long distance shooting with a free floated barrel and appropriate optics. That's the reason ARs are so popular.