I'm not sure this is his best season, despite the OPS+ blowing all other away. Within the context of a down offensive season by the league, maybe it should be viewed as the best.
As far as RISP and Men on Base, the sample sizes are rather small, but not insignificant. To cite the .236 BA w RISP without mentioning his .368 OBP hides all the BBs, he's taken. The decent .462 SLG gives him an .830 OPS. Once you take away the BBs and SFs, he's had just 106 ABs w RISP and has 45 RBIs. (Check out other years below my Men on Base point.
He is hitting .296 w Men on Base, with a .382 OBP, .565 SLG and .947 OPS.
216 ABs and 61 RBIs.
Many view 2019 as his best season, and he did do much better w RISP, but with a lot more ABs. His Men on Base numbers were mixed, but also more ABs:
RISP (152 ABs) .336 BA, .387 OBP, .566 SLG and .953 OPS
Men on Base (275 AB) .320, .368, .535, .902 and 93 RBI
How about 2022, maybe his other top 3 season:
RISP: 125 ABs/55 RBIs (.256 BA, .377 OBP, .496 SLG, .873 OPS)
Men on Base: 235 AB/76 RBI (.298/.380/.557/.938)
Your point is well taken, but with spread out sample sizes of 125-235 ABs, one would expect some differentials. I'm not sure we can read too much into them.
Here is an interesting way to look at RBIs and Devers.
Career: 632 RBIs in 4111 PAs and 3712 ABs
That's an RBI in 15.4% of PAs and 17.0% of his ABs.
2024: 15.4% of his PAs and 17.7% of his ABs.
Hmmmm....