wrong is "how much do you spend now and how will that change (or not change) in retirement?"

Plenty of studies that show 25x your annual expenses is enough to retire on assuming a safe withdrawal rate of 4%. The most famous is the Trinity Study which has been updated from the original. This assumes inflation and was modeled through every year of the stock market's existence.

What retirement planners and calculators get totally wrong is understanding what your current standard of living is and how that may change (paying off the house, kids leaving, downsizing, etc.). For example, if your household annual expense is $40k then you "could" pretty safely retire on $1M. I can point you to about a dozen blogs and people who have done this very thing over the past 3-5 years and numerous others that lurk and don't broadcast it.

Many of them don't "retire" in the traditional sense, but it affords them the opportunity to leave their corporate 9-5 and only do work if they want to, or work on passion projects that they have the freedom and flexibility to pursue.