Feelings about Bassitt aside, the fact that he's a grinder, a great clubhouse guy, willing to do whatever it takes and shove his ego aside... from a pure skills/cost perspective, is there really room for him?
He's going into his late 30's, while his stuff and location has remained steady-ish... would it really be surprising for that to decline a tick or two next year? That's question 1.
Question 2 - what's his role? Backend starter or swingman? In either case, what level of money are you wanting to commit to that role? It sure wouldn't be 21 million per year. So... what do you offer him...10? 10m would be fine for a backend starter but for a swingman??
Question 3 - is there even room for him as a backend starter or swingman? Berrios is already performing like a 4/5 at his #2 salary. Lauer is probably going to slot in the rotation at around 5m. Is he a #3? Is he a 4/5? How much can you rely on him being the version we saw first vs the version we saw in the latter part? Somewhere in between?
The way I see it right now, Gausman in the #1, Yesavage is the 2, Lauer is probably the 3 and Berrios is the 4, or call berrios the 3 and Lauer the 4... whatever. That leaves one spot open and the rotation doesnt need a #5, it needs a #1 that shoves everyone else down. Bassitt isn't that, so I don't think there's a spot for him in the rotation, really. And you don't want the kind of salary he's going to command in the pen.
As much as you hate to lose him in the clubhouse, he doesn't really fit on the roster unless he agrees to a major pay cut and a drastically reduced role as a swingman / fill-in starter. I doubt that happens. Time to move on from Bassitt.