Outside power though does not = power inside the tower. Even if he is the weakest outside, it doesn't mean he's the weakest inside, he could be the strongest. For all we know some or most of the Family Heads could follow that pattern. Bam seemed weak outside, even when getting in at first glance he seemed weak, but he's busted. Similarly though, even if we speculate that Urek is equal to pentaminum outside the tower, it does not mean he is equal to him inside the tower. For all we know their powers manifest differently once inside the tower. Outside the tower penta could just be a bloke equal to a radiant one or 2 at best, but inside the tower he's someone that can alter reality itself, Urek could be someone capable of altering reality itself outside of the tower, but inside he's just someone barely on par with a guy that hid under his bed when penta raided his palace.
We're going to have to wait and see how siu does the scaling but I still keep Enryu above Urek, by a long shot. The only thing that changes is that now I can firmly hold my belief that Enryu is the true #1 in the tower and not penta.