> all interest rates are endogenous: determined by fed policy or future expectations of fed policy based on macro variables

The Fed frames its policy response in terms of the somewhat nebulous natural rate, which implies that there is some exogenous component to rate policy. Additionally, rates have consistently trended downwards for 500 years, well before the invention of central banks [0], supporting the notion that rates are driven by exogenous factors.

[0] https://econreview.berkeley.edu/the-long-decline-of-global-i...