With relief pitchers the sample sizes are just too small. It's forever been the most unpredictable position on the baseball field.
More than the other positions, I think successful relief work comes from routine, familiarity and comfort level, with the team, manager, coaches, stadium, catcher, culture, atmosphere, etc. Can't really analyze that and it could be why the relievers who came from the organization are doing fine and the ones that don't, aren't.