You are very very right, its really about replacing work income with passive income. That can be a pension, annuity, pulling cash out of a 401k, SSI, rental property income, et al. Heck, the gf has a decedent IRA that provides a couple grand a year in RMDs, even that is a little something.I know a few "financial" people have tried to tell me that my wife and I are behind in our number. When you own rental property (especially farm ground) that "number" is not a valid thing. Why I go for lining up replacement of my income. It does get tempting to just liquidate everything and retire today, but I don't have enough hobbies and enjoy what I do. I would actually make a little more if I did that but I'm content now so I will just keep plodding along.
I think because the large majority of people don't have those things, its easier to just shortcut a retirement savings number (or multiple). But yeah, if you want 100k of income to replace, but can get half that off the family farm rental, then you need half as much in your nest egg.
WRT your comment about enjoying what you do- totally agree. I really enjoy about 50% of my job, and the other 50% is people mgmt blech that is less fun. My "retirement" might be transferring my salary to someone else to run the people, and I will just do the fun parts and maybe work half days or something.