The very first time my wife shot my AR-15, she shot it very well. After the first 20 round mag, she was making 300 yard shots on a 12 inch gong. She could hit the 100 yard gong shooting rapidly.
More so than any other rifle, the AR-15 design is very easy for beginners to shoot very well. And THAT might be the clearest defense of the AR-15 ergonomics.