It is the coaches job to make players better......not sure how to not put blame/credit on them when things go badly/well. That is their job, to make players better. I doubt anyone here is absolving any pitcher from having "blame", but saying the coach is not at all accountable, and it is only the player? What is the coach for then?
For me, it can be a case by case thing. Like I said before, I don't blame the Twins for Worley's failure or success - I think Worley has always had the potential to be good, but he is a bit of a head case.
My biggest criticism with the Twins' management style overall is that they give very long leashes to players with ML-experience, but will send down the young players or let them rot in the minors for years (Slama) without getting a chance to fail in the big leagues.
They've been very stubborn about re-building the team, which has resulted in lots of at-bats for guys that won't be wearing a Twins uniform when they do make it back to the playoffs some day. The guys that will be there will have less ML experience than they maybe could have had....
It's all guesswork and assumptions from me, though - I think Worley's problems were Worley's. There is some amount of evidence pointing to the Twins recognizing the issues early (april 2013), and acting accordingly (they sent him to AAA to work it out, then when the issues remained in Spring Training they cut their losses.) .