The question is largely meaningless as it's cultivar dependent. Growers get 26-30+ % THC regularly with contemporary autos. Certainly, there are more high THC cultivars in photo format than autos, but there are more photo cultivars overall.
And this is based on the (IMHO) flawed assumption that THC alone drives "potency" - however that's defined. Terpenes (and probably other classes of organic compounds like phenols and flavonoids) are involved too. That's why from my personal subjective experience certain cultivars have a stronger effect on me (i.e, are more "potent") that others despite having lower THC levels. IMHO, YMMV, etc.