I think it is more valuable in interpreting a pitching coaches' job performance to look at the collective performance of the pitching staff. So, while some individuals may have performed well under Dubee, others were terrible . This can be attributed in part to having bad pitchers to start with, in addition to injuries, and inexperienced replacements but the pitching coach must factor in somewhere. The relationship between the raw skill of the staff and the impact of coaching on the staff is difficult to unravel though. I don't have time to do the research, but there must have been a team at some point with around the same level of pitching talent that the Phillies had, with a pitching coach who had a history of good results that we can use to roughly demonstrate how coaching effects pitching staff performance.