Check again. Powe was significantly better than BBD last season in nearly everything he did. He's also a much better athlete. I wouldn't trade Powe for Ariza, but I would trade BBD.
I also don't get where the "BBD has a higer ceiling" comes from. Seems like it's mostly due to people not wanting to admit that Powe is simply better, so they add that to BBD's description. I don't see it. Powe is and always will be a better athlete. Powe was always viewed as an incredible talent, and was better in college. The only knock on Powe was whether he'd regain his athleticism after his knee surgeries, which he has. Coming out of high school he was considered the #2 prospect behind Lebron. Upside has always been there. BBD's ceiling is less than Powe's and his question marks linger longer.