I hate it. We absolutely don't "know" the things you're saying that we all know. We know that this team had the talent to be the best team in baseball over a 130+ game stretch. We know that for some reason they underperformed wildly over the last 30 games.
We also know that human beings tend to make narratives ("They drink beer in the dugout", "they don't want it enough", "Francona is too nice", etc) to explain random statistical variance. We also make narratives that are accurate. But we know from Bill James and others that pretty huge random swings happen--and not ridiculously uncommonly--for no reason at all.
So, it's possible that a trio of pitcher's sullenness blew the season. But it's equally likely--perhaps even more likely--that September was simply hard luck. ...
Really, given what we KNOW--results-wise--I'd rather go into this spring with exactly the team we had going into last spring than with a team randomly shaken up for weird armchair psychology/"something has to change" reasons. Obviously that can't happen--even before any decisions were made, players are older, contracts are a year later, etc, and obviously Theo and Tito are now gone--but the unmitigated belief that a team that was on pace for over 100 wins into early September is clearly and obviously in need of massive random shakeups seems completely bizarre to me.
I think the equally likely story is that this team was basically a 90-91 win team all along; they played over their heads in the mid-summer, and played worse than that in September. But consider that for most of the season their starting rotation consisted of Lester, Beckett, and flotsam and jetsam, they probably ended up right where they belonged when all was said and done.
The team had two big shakeups in the manager and the GM, but those were likely inevitable. And with any new manager comes a restructured coaching staff, so the McClure hiring is hardly a major shakeup IMO. Nor is it a "make the players squirm" move either. Nor was hiring Bobby Valentine, for that matter, contrary to all the hype.
Looking at the roster moves so far, the team has done exactly what many predicted. Paps was allowed to walk. Ortiz was retained for minimal long term commitment. They added a decent-to-good relief pitcher and a glove-only utility fielder, jettisoned the oft-injured Lowrie and upgraded at backup catcher. As expected, they weren't big players in the FA market due to payroll issues that Cherington essentially inherited from Theo. And now they are seeing if they can further upgrade their pitching via trade. All of these moves were sound baseball moves intended to upgrade roster weaknesses from the previous season.
As for McClure, it's not at all clear exactly how much influence he had over enforcing pitch count limits. Ultimately, it's the manager that makes the decision on pitching changes. If McClure can work on pitching mechanics and the other stuff that pitching coaches do, then that's really all they need; it's ultimately Valentine that has to keep his pitchers fresh over the course of the season.