So that's the only flaw, that index funds weren't widely...

So that's the only flaw, that index funds weren't widely available until after 1976?
Even in 1896 you could hire a broker to manage you portfolio and get close to the index performance.

But, if you prefer, look at the performance of the index against gold since 1980.
Comparing gold to a stock market index is a reasonable comparison. The only "flaw" for gold bugs is that stocks outperform gold.