Sure, but if you look at the chart the 60/40 US/non-US portfolio has only really outperformed significantly since around 2011. That's the last 10 years out of the last 35 in the bottom graph.
The question now is "what happens next?" given rising rates and crazy high US valuations
Historically, the rest of the world handles recessions terribly.
Japan, once an economic engine, is stalled... still.
Europe is aging and they're still stuttering after 08. Don't expect them to make any surprise economic growth jumping past the US anytime soon.
China + other emerging seem like good promises, but china specifically is a huge regulation risk since those companies operate at whim of a government scared of big co's. Also with Evergrande as example, their economy is real estate driven and highly over-leveraged which seems like a major risk to me.
All in all, i'm personally keeping investments in america unless i see real ex-us promising growth. So i think "what happens next" is the global rich keep their money in US assets while they slosh around desperate for returns and speculative investments trying to beat inflation. So... imo more of the same but more stressed this time :)
https://bit.ly/3n6dE6t (Citation to PV)