The argument has no heft at all, because it ignores the laws that require actually funding a defined benefit pension plan, such as ERISA 1974 and PPA 2006, which exempt taxpayer funded pension plans from any and all funding requirements.

The private sector abandoned the model because the promises only made sense with fantasy accounting, and once that was reigned in, they didn't have the power to tax future generations, so they naturally went away. Also, the government pays under market for labor, because the government employee unions prioritize not being able to be terminated today and deferred compensation over higher, market rate compensation today.

It's a moot point anyway, since nearly free target date mutual funds and index ETFs exist where you can get all the benefits of stock market gains without any of the agency risk and cost of pension fund managers and employees. They have been obviated.