Is it as simple as this:
Bob Boughner= good @ power plays?
Dave Barr= Bad @ power plays?
SJ while Bob coached the SJ PP had several years of 20% PP (good for top 10 territory)
Dave Barr had several years of 16% while coaching the Panthers PP (in bottom 5 territory)
I have not watched any of their games but maybe the change in power play is a big reason why he is down. The entire PP was tilted toward Burns the last few years IIRC. he scored 50% of his points on the power play!
60P/31PPP
75P/37PPP
76P/33PPP
Very few players put up 50% of their points on the PP. Their was heavy writing on the wall territory here. Jumbo Joe is old, Marleau is gone, new PP scheme/coach, unsustainable scoring levels ( not that he hit 70P but that he could maintain that level 2-5 years in a row)