I'm going to push back against the 'massive turnover' narrative because I don't think it is accurate. I believe Henry and Werner can be dinged for not backing Theo Epstein sufficiently - they should have given him power over the entire baseball side of the business and had Larry Lucchino back down. The Dave Dombrowski hire was more defensible - Ben Cherington had led the team to consecutive last-place finishes and made several disastrous signings (or didn't have the clout to push back against whoever was pushing those players onto him). Many of us saw Dombrowski right from the start as a hired gun who would maximize a short-term window of contention but was not the guy you wanted to build the team back up after that. John Henry wisely realized that too.
Below those top-level executives, there has been remarkable stability throughout this ownership's tenure, both after Epstein's departure and as the current presence of the 'Gang of Four' has shown. Yes, they had a few promising young execs move on to work with Theo or land their own GM gigs but that IMO is evidence of a good organization and not a black mark.
Out of curiosity, I looked up the GMs/baseball ops heads of other teams during the Henry ownership timeline (so 2002-present) and totaled them up. I did count interim GMs and people who came back to the same position separately, so yes, Mike Port, Hoyer/Cherington, and Theo 1, Theo 2 were counted as 4. But I counted other teams the same way, and the point was to look at instability and upheaval, since it caused PR problems and we lost FO guys at every juncture (Byrnes, Woodfork, Lajoie, etc.) and I'm sure other teams did too. Anyway, the number of GMs each team has had since 2002:
1: NYY, COL
2: CHW, DET, KC, OAK, TEX, MIL, SF
3: CLE, WAS, CHC, PIT, STL
4: TB, TOR, SEA, MIA, PHI, CIN, SD
5: BAL, MIN, LAA, ATL, LAD
6: HOU
7: BOS, NYM, ARZ
That's some fine company there. And of the 9 teams that have had 5 or more GMs in that span, 6 of the 9 also had ownership changes somewhere in there, which often leads to a GM departing (incidentally, 5 of the 7 teams with 4 GMs also had ownership changes). The three that did not have an ownership change and yet went through 5 or more GMs were the Red Sox, the Orioles, and the Mets.
Four titles in 18 years speaks for itself, but it is a bit odd.