You can buy target date funds to minimize how much you have to manually reallocate between equities and bonds, and you can buy an annuity from an insurance company to guarantee a certain income.
I do not understand your distinctions between liability and cost of a DB pension.
> The cost of the plan can indeed be gamed, but there's not much point. It's just an actuarial calculation with all the assumptions that entails, and the actuary shows that long term, investment of this amount is sufficient to cover all costs.
There is a point…to contribute less than necessary for the pension plan to have sufficient funds, in order to make benefits appear cheaper today. For private company DB pension recipients, this results in them not being paid, hence strict laws like PPA 2006 and ERISA 1974. For taxpayer funded pensions, politicians just continuously increase taxes, so it is not as apparent of a problem.
For the DB pension recipient, they have the risk that the DB pension sponsor will come up short, either due to incompetence or corruption. That is a cost. Even taxpayer funded DB pension recipients have had their benefits cut when state and local governments could not come up with the cash.
Unless I had a federal government DB pension, I would assume there is nonzero risk of benefits being less than expected. Also, as a US resident, I have no doubt that even CPI adjusted benefits will be cut in real terms due to impending demographic issues and that is just how the game will be played. Feds will bail out equities over and over, and people with fixed incomes will continuously have less purchasing power.
Either way, I would rather own the assets being bailed out directly so that I can gain the most from the bail out, rather than pension fund gaining it and then still giving me a fixed benefit.