The problem with this analysis is that it does not consider the wealth of these Americans in the context of the American GDP. When you look at who the richest Americans were in terms of the fraction of the GDP their wealth represented then adjust it for inflation, the richest of the rich were in the robber-baron days.
The two you cited, Astor and Rockefeller, rank fourth and first in American history, with 2006 adjusted wealths of $110.1 billion and $305.3 billion. This, of course, blows Bill Gates away, who would rank 13th. Everyone in the top 10 except Sam Walton died before World War II.
This says a few things. First, there are mechanisms in place in the present that prevent Rockefeller levels of wealth accumulation. He would be such an immense outlier today, that it is clear the game has changed, so using Rockefeller as a datapoint to determine when a trillionaire will arise seems questionable. It’s also noteworthy that his $305.3 billion would still be a far cry from $1 trillion.
There are likely many factors at work here. Legislation, globalization, the diversification of the global economy into industries that didn’t even exist in the 1800s and 1900s, the very nature of fossil fuels as a “cheat code” in the game of economic growth, and so on could continue to diminish the ability of an individual mogul to dominate as large a percentage of global wealth. This will stall the coming of the first trillionaire and, if you look at how we’re over an order of magnitude away from having one right now, it could still be a while before we see one.