It has less to do with the recovery than it has to do with still Kopech ultimately being an unknown, PLUS coming off surgery. Let's say Kopech came into 2019 healthy. If the Sox had designs of competing, penciling Kopech in at the number two or three spot still could be a recipe for disaster.
Now add in, say, a 10% chance he doesn't come back right from surgery on top of all that and now competing and going into the season with Kopech as your #2 or #3 starter are likely mutually exclusive ideas.
Maybe he comes back and is immediately a horse. Well, then great. Now you have extra depth. But you absolutely cannot count on that. From a roster construction standpoint he’s a backend starter until he shows you he’s not.