I would happily have a decade of declines or stagnation on the 10's of 1,000s in the kids account over the next 20 years - they can then invest in their productive earning years in companies trading at p/e's of 10 again.
The anti-correlation between bonds and equities hasn’t been a thing for decades. That is advice that passed its sell-by date a while ago.
The modern version is to go hard into equities and out-grow the drawdown risks. You still want a couple years of burn in treasuries but that is strictly a buffer against adverse returns. By the time you retire, the treasury fraction is a tiny fraction of the total by virtue of the equity growth rate.
I don’t have any reason to think that international economies are not correlated to the US. But also I don’t expect them to be that successful. Europe and South-east Asia have a mafia like relationship with their established businesses and regulate away new ones.
The sibling comment addresses bond funds.
ZIRP, 2008, Covid, trump, big tech, and AI all came after Boyle.