I don't like this market cap against GDP measurement. The multiples in Market Cap in those era would be significantly lower. If we look at P/E of S&P 500 [1], what used to be peak PE of 20 a century ago are now considered normal.

So adjusting for all that Rockefeller would still be richer than Elon.

[1] https://www.multpl.com/s-p-500-pe-ratio