Pomeranz was also the 5th overall pick, it's not like he's some scrub that wandered in off the street.
Sure, there is risk, but there was risk associated with every available pitcher.
Also, you can't say "well they could have gotten him if they didn't give up Espinoza, they could have just given up pitcher A, B and C." Unless you were on the call, you have no idea. And honestly, Pomeranz is worth far more than Hill who has already been on the DL, is almost a decade older and is only under control for this season. Pomeranz has infinite more upside than Hill.