There is no question that Farrell has had a major positive impact. I don't think I read posts from folks contesting that. However I don't read every post.
There are some elements outside of Farrell's control that have also helped I am sure. I suspect that as important as the guy that is here is the guy or guys that are gone. Beckett had become a truly negative influence on the other pitchers and his position on the team made him hard to ignore. More importantly while Farrell is a competent, good manager, he was replacing the complete and utter antithesis of competent and good as a manager. At the point in time when the Sox hired him, Bobby V may well have been the worst managerial candidate available as opposed to the best. He was quite possibly the only manager in my history of watching baseball that has forced me to acknowledge how damaging he was to his team of players. In fact Beckett while not being a positive influence probably enjoyed even greater influence with the pitchers since the manager's office was such a black hole of deceit, deception and incompetence. In truth, as often as we have given the Sox, their players and their organization a pass, the biggest pass ever granted was the pass granted for having brought V here. I think we were all so happy to see him go that we just did not care to truly offer up the degree of criticism the Sox deserved for bringing V here. May they never again convince themselves that the opportunity to hire a caretaker for the manager's position also affords them the opportunity to bring somebody in that draws even more media attention than you would expect for a MLB team, especially the Sox.
Lastly. both guys, Lester and Buch were likely as ready as they could be to turn a corner. Farrell and Nieves got them at just the right time, when both players were motivated to live up to their potential. I think both guys feel like they had dicked around long enough. While they had both enjoyed OK careers to that point, neither has really done more than whet both their and our appetites for more. I would not want to leave the impression that IMO the god of pitching coaches arrived and rescued these two guys from themselves. I think their own contributions to their turn arounds are as important as Farrell's and Nieves'.
I think Lester is set. As long as he stays healthy I think he will have a great year. I don't expect him to go sawing through opposing hitters like he has so far for an entire season but I think he will have few off days and his health history is excellent. The only question for Buch is the one about taking the ball for an entire season.