Wow, that’s pretty sad, and I suspect way too common.
I too prefer to assume minimal returns, and zero SS. However I’m old enough now that I do think that SS will provide a portion of what I am promised, so I’m starting to be cautiously optimistic that I’ll get about 2/3 of the estimate. I cannot fathom planning to earn 8-10% on retirement funds (I certainly think it’s doable for shorter time periods, and of course I’ll be trying, but that’s just unreasonable long-term planning in my opinion). 6% is the upper end of what I use as an expect, but again I hope I’m very wrong and pleasantly surprised.
The FireCalc backtesting method IS quite reassuring, I’m just not convinced that it will hold up. We’ve been through an industrial revolution and a tech revolution that have created great gains, but will the automation revolution help or hurt? Probably help the early investors and the well educated, but I do fear for the availability of decent jobs for the majority of people which could lead to overall economic drag and market lethargy.