Why does this matter? It's kind of a meme around here, and I'm curious as to why.
Well, to take my own question seriously, the answer is that not having a core RH middle of the order bat would make the Sox lineup vulnerable to LHP. But is that true?
Devers and Casas each have only a small .050 OPS swing against LHP. As far as the rest of the roster goes: Story, Rafaela, Wong and O'Neill are all RHH. The bench has Reyes and (eh) Dalbec. Refsnyder and Grissom are on the IL but on a path to return. That's a full lineup of RHH and two powerful LHH without significant splits.
So where is your concern to get a "core RH bat" coming from?
Edited down to reply, but I think it makes them quite susceptible to LH starters but it also really neutralizes the entire middle of the line up if an opponent wants to bring in a LH relief pitcher in the biggest spot of a close game (likely facing the middle of the order as the highest leverage situation). This will probably be exacerbated on the road as well, away from the Wall in left.
I agree it wouldn't matter if they all could be expected to hit LHPs the way Casas has (and assuming he learns how to handle sliders) and I think he's going to be fine, but they don't...
Looking at the top portion of the line up (generally speaking):
Duran has a .586 OPS against LHP in his career.
You actually have Devers numbers overall incorrect - you're looking, or at least cited, his career against LH starters only. Overall against LHPs he is a .748OPS hitter (which is .150 below his numbers against RHP).
https://www.baseball-reference.com/players/split.fcgi?id=deverra01&year=Career&t=b
Story I'm not sure what to make of. His career vs LHP on the road is still pretty good (118 wRC+) but starting with the 2020 season (for whatever that's worth) it's been 105; 98; 68; and -25 (he's had 5 AB in such a situation this year). To be optimistic, lets throw out 2021, 2022 and 2023 and assume he's going to be the 105 wRC+ guy on the road but be very good against them at home.
https://www.fangraphs.com/players/trevor-story/12564/splits?season=0&position=SS&split=1.5
Casas as you mentioned, hasn't had much of a split and is an .800 OPS guy against LHP in his young career. Not worried about him.
Yoshida has been a .733OPS hitter against LHPs thus far in his career.
So looking at "comparable" numbers, LHPs have taken the top part of the line up from Duran, Devers, Story, Casas and Yoshida to:
"unusable";
"Alex Verdugo" (Verdugo's career OPS is .766, Devers vs LHPs is .748);
No idea what to really expect on Story, but lets assume beastly at home and "Verdugo" on the road;
Still very good
Below average MLB bat
That is a pretty big mitigation of the ostensible top 5 hitters in the line up when facing LHPs, especially on the road if Story can't get back to the 130 wRC+ he put up but hasn't come close to since 2019. It looks like a pretty big problem at present, and we obviously don't know what to expect from ATM.
*Sorry for the "toggle" between wRC+ and OPS but some splits are easier to see on BBRef and some on FG.