Who cares about returns over the next 150 years? Even half that is excessive. Someone investing at age 18 might care about the subsequent 50 years.
It's going to be a long time before some other country takes over the "reserve currency/investment market of last resort" position the US currently has. No other market is even close to providing the deep liquidity and rule of law the US market has over a wide variety of instruments.
Sure, someone will eventually take over that role, but there are no candidates today. And, to your point: it was clear by the late 19th century that the US dollar would displace Sterling, but it took another half a century for that to happen. On the scale of current human lifespan, you can assume it won't happen at all.
It's going to be a long time before some other country takes over the "reserve currency/investment market of last resort" position the US currently has. No other market is even close to providing the deep liquidity and rule of law the US market has over a wide variety of instruments.
Sure, someone will eventually take over that role, but there are no candidates today. And, to your point: it was clear by the late 19th century that the US dollar would displace Sterling, but it took another half a century for that to happen. On the scale of current human lifespan, you can assume it won't happen at all.