[msdz]

Somewhat doubtful. (The first part of your statement, anyway. Of course the difference between abstract "value" and hard, spendable "money" is a thing.)

Like Mr. Hanson said in my sibling comment, some rulers are (or were!) bound to have amassed incredible amounts of resources. For historical/non-present-day examples, consider looking into figures like Jakob Fugger or Mansa Musa.

[llbbdd]

I have no idea why the adjusted net worth of people who died centuries ago would have anything to do with money in the modern day. And at a glance, neither of your examples had billions of dollars in cash, which is the point I was making. They may have had a lot of value tied up in illiquid investments, which is exactly like Musk's valuation.