I think the OP may struggle to find a solid group of people who could speak to FIREing on 4% and never earning another dollar for the rest of their lives. My wife and I intend to FIRE on 4% very shortly here but I like work (meaning doing stuff). It will literally be impossible for me to live my life, doing stuff, without that somehow turning into a little money at various times.
I don't mean retire and never earn another dollar for the rest of your lives. I mean rather has anyone retired early intending to withdraw 4% of their portfolio annually, and has no other *regular* source of income or financial or medical benefit?
Let's ignore social security because none of us retiring early are getting it for a decade or two or three. I don't factor it in at all.
So, for example, if you retire early on 4%, but your spouse still works and you get your families medical coverage from her employer, that doesn't count. (Medical insurance is our second largest expense, after groceries).
It occurs to me too that a single person with no dependents or a young couple can take more risk and have more budget flexibility than those of us with mouths to feed. For them a 4% or more WR could make perfect sense.
The issue is that you are choosing to overlook social security which is going to be an important part of any frugal person's retirement. What I try to do for "FIRE" is to bridge the gap to social security age which is also around the time that I would start tapping into tax advantaged accounts. There are ways to access the IRA early, but it's easier for me to just look at it saving X amount to fund pre-IRA/Social Security and let the "true retirement" take care of itself with social security and my 401k/ira contributions. If I were to say, stop working at 40, it's hard for me to believe that there would be no income from whatever I happen to be doing with my time from that age to "true retirement age", so there is no worry that the 4% rule won't work over the 22 year period from 40 to 62 when I would then have access to social security, (and shortly after that,) medicare, IRA's etc, is just not something that ever comes to mind because it's not realistic. I'm not sure 4% is the right number for this purpose for myself.
For the 4% rule to work, it doesn't matter how small your family is, it's a very simple mathematical equation and works off your available capital and expenses. I don't know that single person would be able to cut their expenses any easier than a family -a single person already has a smaller budget than a family, so their 25x goal is probably a much smaller number to begin with.
Sometimes I wonder if the 4% is too conservative for my purposes, when we are expecting to do some sort of paid work in 'early retirement'