Increasing taxes for higher contributions to maintain benefit levels does not imply a guaranteed rate of return. It doesn’t even seem like one.My post supported itself - they are considering a 100% tax increase to meet (or guarantee) the under-funded pensions.
This is because the actual return for both the individuals and groups will depend on many factors including their mortality, plan design, final salaries and even the tax code. The final return will vary by individual, and it will vary over time for the group.
Do some calculations for a given annuity with different numbers of payments and see how the return varies.