My limited understanding is that they just haven’t caught up in yield. But I see autos listed in the 20-24% THC range all the time. I think they’re probably plenty potent.
Oh, and fwiw, I’ve only grown photo before, so I don’t really know. I’m doing autos for my next grow, though, so I should have a stronger opinion by the time I’m smoking them lol. You might be right!