I'm confused by this comment. That sounds like a savings account you're talking about. But a T-Bill grows at inflation + (small percentage, though probably still less than GDP growth). And a stock market fund grows faster still (and in general, the stock market has shown sustained growth when measured over decades--though one might question that after the last 15 years). Given an index fund invested in 1929, you would have growth beyond what the economy experienced during that period, right?

There are questions about how you'd manage a multi-trillion dollar fund: you'd eventually reach the point where you can't just use index funds. But other than that, your comment doesn't seem accurate.

Edit: What is true is that there is a limit to what your investment could become. For obvious reasons, it can't be more than the wealth of the world, and there would be asymptotic behavior at even less than that.