Why, in 1972 would one withdraw 100,000? and why would you claim you can't buy much with 100,000 in 1972? In Toronto in 1972 I think one could buy about 4 decent average houses, maybe more. I forget car prices, but I'd hazard a guess at about 3000 for a fully loaded Pontiac GTO.
I guess my point is you are assuming 100,000 is a pittance in 1972, but it isn't. A 100,000 then is more like 625,000 today. And a million then, is like 6.25 million today. There is no way anyone in 1972 would realistically need to withdraw 100,000 a year in order to live. BAck then, somone earning 20,000 per year was living high off the hog.
The point of starting in 1972 was to show the sequence of returns problem that occurs when you are withdrawing out of equity. I realize that you'd have to inflation adjust these numbers, so the starting $ value would be different. That doesn't change the result... either way, if you withdrew 10% of the value you would quickly deplete all capital. The absolute numbers weren't intended to be realistic.
My comment about inflation is regarding the rapid devaluation that occurred in those years. You can see it here:
https://www.multpl.com/inflation/table/by-year
Let's say you started in 1972 by withdrawing $20,000 a year. By 1980 you would have gone through some very high inflation years (annual inflation of 9.39%, 11.80%, 6.72%, 5.22%, 6.84%, 9.28%, 13.91%, etc) which would have made the annual $20,000 amount worth considerably less in real dollars. A person would then be forced to increase their $ withdrawal, stressing out their capital and depleting it even faster.
Another example with more realistic historical numbers
The year is 1972, and you have $200 K of capital invested fully in equities. You will withdraw 20K (10%) the first year and then increase your withdrawals with inflation. As you point out, 20K is a good amount of income back then, but due to runaway inflation you soon have to start withdrawing more for the same purchasing power.
This investor completely ran out of money (capital is gone) in just 7 years. If somehow you tighten your belt and don't increase the 20K withdrawals with inflation, the capital lasts a bit longer... 15 years. Note however that 20K purchasing power in 1972 is equivalent to 54K purchasing power after 15 years. Ignoring inflation is not viable. A person can not still be living on just 20K after all that inflation; that's a 60% reduction in real income after those years.
The important point of all this is realize that the 10% CAGR rate of return on stocks does not mean it's feasible to live off 10% annual withdrawals from a portfolio, especially if there's inflation. Both inflation and sequence of returns can work against you, and the 1970s demonstrated that. Investors have been very lucky in recent years to be in both a high performance period of equities and low (almost nil) inflation. This combination can make it look like it's easy to make capital last a long time using a high equity allocation, even with high withdrawals.
Historically, it hasn't always been possible. And personally I would not be comfortable assuming that both low inflation and high equity returns continues.