Hmm, according to this calculator [1], Rockefeller's net worth of $1.4B in 1937 would be worth $28B today.
Elon's is around $240B, so it sounds like 10x the amount.
Even by different calculations, it seems like an order of magnitude is a big difference.
By GDP, they are both worth around 1% of the US GDP, but the US GDP is many times what it was then, particularly post-WWII.
Musk's buying power seems significantly more than Rockefeller's by any metric.