An enormous number of players have undergone Tommy John surgery -- over 80 percent of MLB games now feature at least one -- so we've been able to learn a lot about what to expect from a pitcher his first year back.
The pattern is clear -- a little wildness, often an uptick in velocity, but overall a slight regression from years past. Which is why Zack Wheeler's return has been so notable -- he's almost exactly the player he was prior to his surgery, despite (or perhaps because of) his exceptionally long layoff.
Thus far, Wheeler has been effective on the mound, with a good-though-not-great ERA of 3.72. This is just a hair over his career mark of 3.54, an increase that mirrors the league-wide spike in offense going back to 2015 (his increase in home run rate also reflects this trend across MLB).
Wheeler is striking out a respectable 8.25 per 9 innings while generating 9 percent swinging strikes. That said, he's also still walking an awful lot of batters -- his 3.72 per 9 innings is a slight improvement over his 3.91 for his career, but still leaves a lot of room for improvement...