This FO lucked into finding Reyes and got Urias for a good deal. Previously, they were trying to fill holes with replacement level guys that had zero upside. When you consistently have to do that, rather than use AAA prospects that may have a higher ceiling, you're limiting that value you are providing to your team. For example, if Yorke or Rafaela were in AAA earlier this year, they are likely called up to fill the gaps rather than running to the waiver wire.
The biggest problem this pipeline currently has is high level pitching in the upper minors. It should look better next season as SoxProspects projects the following for AAA bullpen: Liu, Fernandez, Guerrero, Zeferjahn, Politi. That doesn't include guys with prior MLB experience like Robertson, Kelly, Jacques. They may not all work out, but that group could provide a much better spark than what we got at times from Faria, Scott, Lamet, Dermody, Garza, etc.