Spoiler alert: They probably won't be either way. Our population is too small by comparison, we just lucked out in that it took China/India longer to industrialize.
By 1915 America had higher GDP per capita than most of Western Europe - BEFORE WW1. Western Europe had higher GDP per capita than China/India by like 1200 AD. You are so so far off the mark.
Also, India's population only started exponentially growing in the late 1800s. By that point America had already industralized and was already the richest.
Go ahead and put your money where you mouth is, sell all of your US stock, and invest in African stocks since population growth is apparently the only thing that matters.
Edit: Also, the predictions are for next century. Even if they were making the straw claim you believe they are, they probably won't be around to collect on the super-long-term investment you suggest.
Edit #2: Checked out your comment history, looks like you're just a garden-variety racist who thinks that white people are better than everyone else.
I said that the US _lucked out_ in that China didn't industrialize first. I didn't say that industrialization was a product of luck.
If China were to develop to the extent that the US has, which it's on a path to do, then population will absolutely matter. An American company with a market of 650 million potential customers isn't going to hold a candle to a market with 1.4 Billion.
I'd absolutely divest in the US and invest in China if I were going to be alive for another 100 years. Africa wouldn't be a bad bet either... which is why China is already making significant investments there.