In 2008, Baseball America ranked Chris Davis as the Rangers #2 prospect, and said "Davis has taken off as a power hitter in pro ball...Not only does Davis possess well above average power, but he knows how to use it...Davis could be an impact middle of the order bat in the big leagues..."
So I don't see it as a fluke or PED driven. I always assume that the player is innocent until proven guilty, and in Davis case, there aren't even any allegations out there.
Lots of top prospects don't pan out, and fall by the wayside. In some cases, they do. I think BA pretty well nailed it in their 2008 prospect report... and I'm glad I have him on one of my fantasy teams (wish he was on the others too..)