I think it's Casas + Kutter for Alcantara and then Bregman.
1. The fact that the Red Sox have been in on Bregman and Arenado at all can only mean that they do not view Raffy as an acceptable major league third baseman. And agents gonna agent but in the end Raffy is a professional who will play the position he's assigned because he understands the bottom line is winning.
2. Bregman is projected to be a 4.1 WAR player in 2025, equal to Devers and higher than anyone else other than Crochet. The idea that he's in decline is exaggerated. Yes, he probably won't ever be the player he was in 2017-2019 again but there's no reason he can't continue to be the player he has been from 2022-2024. His statcast profile doesn't suggest declines in any of the areas you'd look for aging related decline.
3. Crochet-Alcantara-Buehler-Houck-Bello-Giolito would be an insane rotation. It has the depth to go a full season and survive injuries and also terrify a post season opponent.
4. Yes I think you go six man, I think six man has been the way to go ever since
rosters expanded to 26 in 2021. The benefits of increased rest and reduced injuries is totally worth it if you've got the talent to pull it off.
5. A rotation like that deserves a real defense, and Story and Bregman have the potential to be huge as the left side of the infield for the Red Sox, in addition to our potential three gold glove outfield. Those plays Raffy doesn't make at third base not only mean additional runs but also more wear and tear on our pitching.
6. Kutter and Casas are both valuable but they are completely expendable in this scenario, or any other scenario in which you add an upgrade to the rotation or third base defense. Miami is not going to be competitive this year and there's no reason to waste another cost-controlled year from Alcantara. If they prefer to think further into the future you can always get another team involved.