At the big league level, it's more about between the ears than mechanics. That's not to say tweaking a guy's mechanics aren't addressed from time to time. But (and this makes me wanna mouth-vomit) I agree with LT on his point about when guys get up to the show, they pretty much have their shit dialed in mechanics wise, classic delivery or not. On his point about which pitching coach has really made a difference, consistency-wise, for some guys, I would suggest Dave Duncan, Leo Mazzone, Roger Craig, Dave Wallace, Rick Anderson, Rick Peterson, Joe Kerrigan, John Farrell, Orel Hershiser, Bill Fischer, Bud Black, Larry Rotschchild, Marcel Lachemann, Galen Cisco, Art Fowler, Mike Maddux, Ray Miller just to name many. I'm well aware that most of these guys also had some studs to coach in their time, but most of these guys were also able to crowbar some pretty nice performances from some otherwise nondescript pitchers. Examples? Here ya go:
Duncan: Pineiro, Lohse, Kile
Mazzone: Neagle, Burkett, Ortiz, Wright
Craig: Reuschel, Mike Scott, Donnie Moore
Wallace: Martinez Brothers, Hershiser
Anderson: Hernandez, Pavano
I would love to keep Googling, but I gotta split...I guess my point is, I like Mike Butcher. He will always have equity with me because of the way he handled the Adenhart tragedy, but I don't think he is a difference maker as a big league pitching coach. And I don't think it's about helping with a guys delivery, I think it's because, from what I heard, (Jepsen is a Reno guy, he's a friend of a friend, and it may be BS) he's an asshole. we've seen glimpses of it in some of his soundbites ("I sleep just fine"). Who knows for sure about that part, but I can't name one guy who came here and either:
A. Got Better
B. Continued his previous trajectory (outside of Pineiros 1st year here)
I could be way off, I'm on vacation, I have had a few beers.