Id agree, there is no reason an auto couldn't equal or even out perform a photoperiod. If you ran them side by side for the same number of days the autoflower yield and quality would well exceed the photos (which probably wouldnt have even finished flowering).
The only "benefits" ive seen from growing photos is
1. They are more forgiving to newbs, because you choose when to flip em. So a week of stunted growth or some nute burn isnt as big an issue because you can just wait till they recover before the flip to 12/12.
2. You can try more high stress techniques to train em, topping, scrogging, lollipopping, etc (if your into playing around).
3. If you grow out a particularly nice phenotype, you can leave some bud on, reveg, and take clones to keep that pheno going.