Paying JD more than he's already owed by the Sox is a huge gamble.
He's getting older.
He's had back issues.
He's pretty much just a DH, now, and playing him in the OF risks injury.
He will not likely make more than $23.75M a year on any new deal, but the $2.5M buyout makes it so he only needs to make $21.25M to break even for 2020 only. There is no buyout, if he opts out after 2020, and his salary dips to $19.375 those 2 last years. It may make sense to opt out after 2020, but a bad injury could be a risk he does not want to take.
So, he's owed $63.25M/3, assuming he stays for all 3 years. Is it worth it to him to sign for $70-75M/4? That's basically adding $7-12M for one more year. Maybe, the Sox could be the one offering the most for a 4 or 5 year deal. I'm not sure anyone offers him $80M/4 or $90M/5.
If we got him back for $72M/4, the AVV would be reduced from $22M to $18M. $76M/4 would be $19M, and so on...
I'm not sure saving that much on the AVV and luxury tax budget is something the new Sox management is even considering.