Opportunity plays a role. No one on the team had even 600 PA (68 major leaguers reached that lofty threshold in 2025), but Larnach led the Twins with 567. Being third in RBIs seems like a black mark, not a gold star, for a guy whose only value is with the bat.
In fairness, he did bat leadoff 14% of the time and in the 2-hole another 32%. But even in the 231 PA he batted 3rd or 4th, he racked up only 24 RBIs - at that rate he'd need nearly 1000 tries to accumulate 100 RBI.
Teammate Byron Buxton achieved 83 RBIs in fewer PA; that's a bat that would be hard to replace. Jo Adell of the lowly Angels (hardly a run-producing powerhouse franchise) managed 98 RBI in his 573 plate appearances - maybe hitting 37 HR instead of Larnach's 17 had something to do with the discrepancy.
There were plenty of players who produced RBIs for the Twins at a similar rate to Larnach. If he were gone, the plate appearances would be spread around and you'd never notice the difference, even as the roster stands now. Cody Freaking Klemens (a player I could hardly be accused of woofing for) would help fill the gap, for instance - Ty France did better too, and he didn't cost what Larnach is about to command in salary.
Don't use RBIs as any kind of defense of Larnach's value in 2025. And if as you suggest he's not easy to replace, to say nothing of improving on? That would be a black mark on the FO.