FanGraphs did their positional power rankings for SS.
Padres: 6th, 5.1 fWAR
Sox: 13th, 3.6 fWAR
Boy, this would look better with Trevor Story. Hernández pulled off a neat trick by turning into an excellent defensive center fielder in his first two seasons in Boston, but he’ll have to do it again at another up-the-middle position this year in the wake of Story’s potentially season-ending surgery. He’ll also need to get right offensively; a severe power outage led to a miserable 75 wRC+. It seems to be more pitch selection and consistency related than a loss of ability to drive the ball, which explains why our projections expect a return to normalcy, but that’ll be something to keep an eye on as the Sox try to cobble together a solid shortstop out of two part-timers.
Mondesi is that second part-timer. While Hernández will split his time between short and center, Mondesi will split his between short and the injured list if history is any guide. He’ll miss the start of the season rehabbing the ACL he tore last year, and even when he’s back in action, he’ll be a mystery box: he’s hardly played in the last two years, so projecting his output is wildly speculative. He’s always been a brilliant defender, but his offense has never quite come together. Boston is hoping he’ll fulfill the promise he showed early in his career. Even if he doesn’t, though, 280 plate appearances of competent defense would do quite nicely.