I think you miss the Epstein quote's meaning here. Bill Parcells put it another way - that each season is its own thing, not a continuation of last year. Chemistry appears when demonstrated success appears. You bring in a bunch of high character guys who suck at baseball and then pile up a 3-17 start, chemistry ain't happening. You do want to change a team's energy each year and try to keep improving. That will rarely happen with zero turnover. What did Epstein's change mean? It meant a playoff berth in 2005, an honorable season in 2006 and then another title. In a sport as fluky as baseball, I don't see what the complaint is about the results.
Can you replace Napoli? Hell yeah you can. It might take a platoon formula like they did for LF, but of course you can cobble that together. The Red Sox 4 FAs are ALL replaceable, but there is some risk and/or tradeoff surrounding each one. I think the org is happy to give young players a spin here - but there is also a lot of money flowing and they will have a chance to improve. I think they could be in on Tanaka just because outside of Ellsbury and Cano there is no All Star talent in this year's free agent crop. I am sure there is commentary about loading up for Stanton, but yes - as a corner outfielder with an injury history of sorts - that is a risky guy to throw the system at.