They added pieces, but had much more IL time in 2022 (Story, Eovaldi, Wacha, Hill, Kiké, Devers, Houck, Whitlock). In 2021, they had a largely injury free year.
https://www.overthemonster.com/2021/10/26/22746015/boston-red-sox-starting-pitching-injury-nathan-eovaldi-eduardo-rodriguez-nick-pivetta-tanner-houck
Rotation health was the engine that drove Boston’s surprising success
It was the biggest surprise and provided key stability.
I’m not sure if you heard the news, but the Red Sox were a much better team than anyone expected before the season. The projection systems largely saw this team maxing out their win total somewhere in the mid-80s, and speaking personally I was even lower, predicting they would finish the season below .500. We know what happened instead, and there were a lot of reasons for it. We’re surely going to dig deeper into some specific points where real life diverged with the projection systems for the 2021 Red Sox, but to me there was one big picture quality that led them to their heights above all else.
The starting pitching health for this team was both the biggest surprise for this roster as well as the most important factor for their surprising overall success. Even before the season with my low prediction, it was with the specification that there was no way this rotation was going to stay healthy. That is not to pat myself on the back because my prediction was still extremely wrong, but rather to illustrate how it was essentially a foregone conclusion that this team was going to suffer blows to their rotation hitting the injured list. Instead, none of their main five starting pitchers hit the non-COVID injured list.
That certainly is not a reason the team can care a little bit less about starting pitching depth, something that presumably would not enter their mind. It’s hard not to give the organization some credit here for succeeding where so many other teams did not in 2021, and where they really didn’t have any right succeeding given the injury history of the pitchers in question. But even if it was just a lucky year, at the very least it played a major role in giving us much more entertainment than we were expecting in the late summer and into the fall.