There is every reason TO GFIN this year and trade for reinforcements (in first place, high percentage to make post season, all-star central core will begin breaking up after the season and then more radically after 2022, relatively healthy, and with clear clear weaknesses). No better set of justifying circumstances than those.
There is no reason NOT go GFIN, EXCEPT ... they don't have enough depth in the system to have competed for the blue chip players being moved.
There will be major turn over after 2022. I suspect the Sox will contend in 2022 health provided, but after that we may be seeing the beginning of a more robust generational rebuild. With the window closing for this superb core (JD opt out 2021, X opt out 2022, Sale opt out 2022, Eovaldi, Vazquez, Hernandez FA 2022), Sox may be at THE END of this era rather than at the beginning of the next one (roughly speaking, I know there's more overlap than that in these things).
The Red Sox will not spend their way through the upcoming transition (they will spend some of course, but clearly want to build from the farm and the farm is no where near what it was under Cherington. It won't be ready with an X, Mookie, Devers, in two years ....(Casas may be the only one ...) .. so, there may be some real rebuilding of ML roster starting 2023. And that will require patience.
This is all to say: if not this year, when? Maybe next year, but you can never assume health. And if not next, could be a little while. So, good year to GFIN.
I think the better framing might be: This is precisely the kind of year to GFIN, but the Sox organization is just not deep enough to make that happen ....