The alfphaantagelive calculator is reporting much lower numbers than the real value.
Yahoo has a symbol for S&P 500 total return: ^SP500TR Check out: https://finance.yahoo.com/quote/%5ESP500TR/chart?p=%5ESP500T...
Punch in December 2000 for start and today's date for end. You'll get 398% total return. 398/21 = 19% annual return.
Total return includes dividend re-investment.
The alphavatangelive calculator says 3.31%, but even without dividend reinvestment the S&P 500 reports 11% average annual gains.
This does not price in inflation which historically reported as 3% over long periods and was much lower until recently.
Damodran has as good historical financial returns summary page: http://pages.stern.nyu.edu/~adamodar/New_Home_Page/datafile/... . According to the spreadsheet linked to on that page, S&P 500 returns with dividend reinvested is 11.64% since 1928. Assuming 4% inflation, that's 7.64% annual returns.
So going all in on the stock market over a long time you can withdraw 7%. Even through world wars, depressions and stagflation periods. Some decades will be better than others.