The thing is, the Sox arguably didn't lose their best RHH against left handed pitching. Refsnyder, who is not retiring, has outperformed O'Neill v LHP over the last three seasons (Refsnyder with OPS against LHP of .941, .828, 1.005 over 310 ABs compared with O'Neill at 1.179, .793, .788 over 272 ABs).
And you forgot Romy who had an .879 OPS against LHP last year. Plus the improvement from a full year of Casas, (.758 OPS last year against LHP, .817 in 2023) a functional 2B, whatever Story can produce, and the contributions of Anthony + Campbell.
EDIT- and Wong's defense is only relevant if it results in him not hit against LHP. There does not appear any plan to bench/trade Wong this offseason, so, his .877 OPS against LHP counts for forecasting purposes too.
More specifically, O'Neill only had 156 plate appearances (over 75 games) against LHP last year:
- Emanuel Valdez played in 65 games at second (with only one game started at another position) and, overall had 36 plate appearances against lefties with an OPS of .296.
- David Hamilton played in 39 games at second and, overall had 50 plate appearances against lefties with an OPS of .532
- Dom Smith played had 50 plate appearances against lefties with an OPS of .663
- Bobby Dalbec had 39 plate appearances against lefties with an OPS of .291
- Garrett Cooper had 43 plate appearances against lefties with an OPS of .645
That's 218 plate appearances against LHP with horrible production. O'Neill only had 156 plate appearances against LHP all year. Just having a competent second basemen plus Casas would make up for most/all of the loss of O'Neill.