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.
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.
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.