It's hard to compare people who lived under vastly different economic systems. I would also put people who were the leaders of their country into a different category: the line between what they own and what is part of the nation's wealth is very blurry. I think even for more recent private individuals like the Carnegies it's a little more complicated than taking assets multiplied by inflation rates. Spending power also comes into it, and you could use another measure like net worth as a % of GDP.

Musk may still fall short in those ways, which is why I made the "ever" a question. Poking around the internet a bit more-- your link & others-- it seems pretty likely. Then again I'm not sure there can really be a meaningful difference in wealth between anyone who was worth the equivalent of > $100B in todays money, however it's calculated. (Possibly you'd distinguish between money on paper vs. more tangible assets. Or some method of distinguishing Musk's wealth, a lot of which seems based on the speculative future value of Tesla than based in its current operations)