Yes, I understand the math. You’re forgetting about the employer-paid portion of the pension contributions (much like Social Security or a 401k plan). Right now, the employer contributions can run anywhere from 100% of the employee portion to about 200%. Again, it depends on the particular financial situation of the employing agency, and their benefit formulas.
And, yes, the benefit amount would be somewhat less than what it is today in most cases. I have no problem with that as long as everyone knows about it up front.
What I have a problem with is the claim that we should retroactively change an employee’s compensation — long after they have earned it, and after everyone agreed to the terms of the agreement.