I'm not sure on how to interpret the question.
Taking it literally, it's too soon to answer, isn't it? If the kid busts, we should have sold it; if not, we did well keeping it.
Generally, it's not smart to sell draft picks unless for strict financial reasons. Phoenix takes a lot of heat, but they probably need to do it in order to keep a high pay-roll and still make money.
Personally, I wouldn't have sold it, because there were still players that I like enough to give a guaranteed contract available (Chalmers, for example; although I don't know a good bunch of the draftees, including Giddens). I believe the FO followed the same rationale. If they had felt that among the players still available none had a good chance of contributing, they would have sold it.
If Giddens doesn't become more than the average min vet swingman during his entire career, the pick was wasted. If he performs like an average min vet swingman next season, it was probably a good decision to keep the pick and draft him. At this moment, we don't know. From what I've read, it's not wild to expect that Giddens becomes a reliable and solid rotation guy, a >LLE <MLE type of player. If that happens, it was a good draft.
For the record, IMO it's unrealistic to expect that any of our picks becomes a superstar. My Giddens' prediction is based on where he was drafted, but Walker would need to improve drastically.