I think this day and age with the new auto strains out there, they definitely are on par with photo plants. Back when they first started out, the thc content was low, so was the yield. But that was when they made the first Lowryder, which was 50% Mj and 50% Ruderalis. Now they have crossed it back many times over and the plants are more like 85% mj and 15% Ruderalis(just guessing %'s), so the low thc of the Ruderalis doesn't effect things as much.
I would have to say that growing conditions probably play a bigger role in THC %. I grew some Narcotherapy autoflower strain last round, and it was by far the most potent stuff I have ever smoked.