Bello might be the best pitching prospect to break Boston's rotation since Clay Buchholz (think healthy Clay). And he's showing glimpses of it at the MLB level. His innings, velocity, and stuff has ticked upwards every single year and he's shown bat-missing ability at the MLB level. Also, as good as Stallings is, he's a defense-first catcher who is a .700 OPS guy career and sub .600 this year. McGuire isn't much of a step-down, quality defense and how much better is Stallings bat?
I like having Bello in the rotation next year, and love the potential he and Whitlock bring there, but having two youngsters also brings a level of uncertainty that really makes me want to strengthen the top of the rotation. I'd love to see a trade for a young cost controlled pitcher. Sandy Alcantara from Florida might be a pipe dream, but it's not like they're going to compete in the next couple of years. An elite prospect package might do the trick.
I'm thinking Alcantara for Pivetta/Marcelo Mayer/Nick Yorke/Ceddanne Rafaella. BTV has this as a slight underpay for us but I think it's fair. Pivetta gives them a good MLB pitcher to replace Alcanatars innings for the next several years and the 3 prospects give them huge future value. I'd offer at least one of Eovaldi/Wacha a QO (if not both). If he was seriously tradeable, you might have to replace Yorke with Bleis, or just add him in.
Alcantara
Sale
Wacha/Eovaldi
Whitlock
Bello
Paxton
There's a lot of potential in that rotation, if Sale gets healthy that's a WS-caliber rotation. That also gives you a core rotation of Alcantara/Bellow/Whitlock that's locked up for years.