as you said there is a big area between long shot and top echelon. The FO is paid to figure out which guy in between will make it and which will be career minor leaguers. That's how good FO's make their money. They trade prospects that never make it for top players.
Edit: I don't dis Ellsbury. I think he is a big talent, but he's probably not ready to step in and produce this season. That's why I'd consider a rent a player for the second half.