Let's go through that list, shall we?
Ian Kennedy 20 game winner last yr, 4th in NL Cy Young voting. The definition of mediocre
Phil Hughes 18 game winner in 2010, elite setup man in 2009, sucked in 2011 and is about to win 10 games prior to the ASB with good peripherals. More mediocrity
Joba Chamberlain was an elite setup man, got hurt converting to the rotation, was pitching phenomenally well last yr before getting hurt again. When healthy, he is an impact reliever
David Robertson is the best setup man in the AL over the last 2 yrs. More mediocrity
Tyler Clippard has been the best setup man in the NL over the last 2 yrs and this yr has turned into an elite closer
Mark Melancon, we know his story, but he was an effective closer last season
Jeff Karstens is the definition of mediocrity, you got me there
Alfredo Aceves was your best pitcher last yr and has been exposed in a role he shouldnt be in this yr. He isnt a mediocre pitcher by any means
Jose Quintana is 4-1 with a sub 1WHIP and a 2.04ERA in his first 8 big league starts. The White Sox don't think he's mediocre