I'm not convinced Betts will be a 9.6 WAR player every year, or that Bradley and Pedroia can keep up that level of production, and Papi is gone. The team and their offense will remain good, but like 5 guys had potential career years, all at the same time (and all remained healthy). That doesn't happen very often.
All I'm saying is that Betts' minor league numbers suggest he may still have room to grow offensively and that it shouldn't be seen as abnormal. Obviously it's very unlikely he gets much better, but he could absolutely a least maintain that level of production. His HR numbers increased, but his BB rate was not where it was in the minors, and his BABIP could actually improve as well. Fangraphs had him at 7.8 WAR this year; I don't think that's a number that will be difficult for him to maintain, honestly.
Pedroia had a year that was in line with what he's always put up. He had a down year in 2014, and this represents a bit of a peak in the 2012-2016 stretch (and he's 33, so obviously he may start winding down at any point), but it was certainly not a career year.
Bradley's numbers overall are very close to what he did last year over half a season and don't stand out as strange given his minor league track record. He also may even have room to grow more still.
Bogaerts, as I mentioned, probably still has room to grow offensively. Benintendi is just getting started. Moncada hasn't really gotten started yet.
I will be extremely surprised if 10 years out, we look back and realize 2016 was a career year for Betts, Bogaerts, and Bradley. It wasn't a career year for Pedroia. And they'll be adding Benintendi and Moncada even as they lose Ortiz and Pedroia ages. I'm just saying, I won't be surprised at all if they have a similar offense again very soon. They're built to hit.