If you are drafting late and forfeiting picks, yes, it will take longer to judge. But when you are drafting as early as the Phils have, you have access to the best players. The cream, more often than not, rises to the top quickly. Very good players usually show they can play from the get-go.
I'm not saying everyone picked in the last 3 years is a bust, but you can compare what other teams are doing and have done to realize this isn't going very well.