Firstly, I'm just trying to understand how it works.
Secondly, in cases where the pension plans liability is reduced, my point is equally valid - just the other way - in that the question becomes why should the employer benefit from the divorce in a DB scenario?
Thirdly, I don't agree with your hypothesis. You are just picking figures that may or may not support your point. I could explore further if required. The essential point is that I could easily pick a scenario where the liability is unambiguously greater when the pension is earmarked for the non-member spouse. Say, the member had left service so no future service and all the deferred pension is allocated to the younger spouse - there is no way that the immediate annuity cost of an inflation-linked single life pension payable to a 55 year old is less than the NPV of a 50% reversionary pension payable to a 65 year old. Do you accept?