"Should the 60-40 ratio be changed, or should Treasury exposure be reconsidered altogether?"

Yessir.

Bringing quite the scoop, this article. Unbelievable:

For decades, the 60-40 stock and bond portfolio — or something close to it — allocation model was the universal standard: capture growth with equities and offset risk with bonds. While investors more often fretted over their strategies for the “60” growth segment, the “40” leg was typically just left to plain old Treasury bonds.

"since 2021, with the return of high inflation, bonds are less and less useful as a diversifier"

And, this:

correlation between stocks and bonds has turned positive, meaning bonds have started contributing to equity losses, instead of offsetting them.

Why?

Nobody knows.

The reasons range from the inflation shock, higher growth, fiscal incontinence, crowding out by hyperscaler debt, to the credibility of the Federal Reserve under Kevin Warsh