Although stock prices may fluctuate significantly, dividends are relatively stable. Dividends don't often fall very much and, in the financial crisis, dividend payments on the S&P 500 fell about 20% compared to the actual S&P 500 index which fell about 50%, and both recovered in short order. With $1M saved up, you will receive approximately $20,000/year from dividends if you invested 100% in the S&P 500 (~2% yield). The dividends rise around 5-7%/year on average so, even without tapping into the principle, you're passive income will rise at a pretty solid rate. Compare that to investing in bonds at 2-3%, you will receive a similar income, but no raises.

Equities are the way to go over the long term and, if you need to rely on selling your principal to sustain your lifestyle, then you shouldn't withdraw at a constant rate anyway. You should withdraw when it makes sense. I.e. sell your equities when the yield is low and don't sell (or even add if you have extra money) when the yield is high. Selling at a constant rate will force you to sell even when stocks crash. You wouldn't want to be selling in a 2008-2009 scenario. When you think stocks are expensive, it might be a good idea to sell a bit more than you actually need, just to have some extra cushion in case stocks do crash.

Most of these ancient financial programs will gradually shift your assets from risky (stocks) to less risky (bonds) as you age, but they usually totally ignore the current situation. Take 2009 for example, stocks were incredibly cheap and if you followed a plan of gradually shifting from stocks to bonds, you would have been a seller of stocks just when they were at their cheapest and a buyer of bonds when they were expensive. That's absolute financial lunacy. When stock prices are low, they actually become a less risky asset class and you should take that into account when adjusting your investments. At that moment, it may have actually made more sense to shift back from bonds towards stocks because they were less risky, even if you were 80 years old.

In the end, it depends what you are comfortable with, but it might help you to study equity markets some more to get a full understanding of how they work, the risks involved, and the return potential, particularly how the risks and return potential fluctuate over time. Your ideal asset mix should not be set in stone, and it should in fact adapt with your age, risk tolerance, and, most importantly, changing market conditions.