You can't really complain what they've done with the pen. I think between Barnes/Schreiber/Martin/Jensen we should be fine late innings, and if the rotation is healthy there's a good chance we see a lot of Crawford/Paxton/Houck in there too. Mid year additions such as Mata could really help down the stretch as well.
The rotation has a lot of question marks, but technically you could say there's a ton of upside there as well. Optimistic view;
Sale comes back, and is a comeback player of the year. Pitches just a hair below elite. Ranked 5-10 in Cy young voting
Paxton comes back and gives you a sub 4.00 era and 120+ innings
Kluber gives you 150 innings + as a solid 3/4th type of guy
Bello wins ROY, the first homegrown capable starting pitcher out of Boston in a LONG time.
Whitlock shows you why he's so great and why the Sox moved him into the rotation.
Houck answers the question about being able pitch deep into games, because of a viable mid-rotation starter.
Pivetta - is good old reliable 4th starter Pivetta.
MYSTERY MAN? a mid-season trade, a pre-season trade, or perhaps a rookie from the minors answers the call.
Sox don't need all of that to happen to be great, and each one is perfectly plausible on its own.
But man, it's really hard to be optimistic after the last few seasons, health issues, and this off season.