> a good APM is a fail safe that compensates for other failures.

Absolutely. The ideal organization would adopt a tool to make squiggles when you do something silly AND have an APM that treats slow pages as bugs AND have a culture of triaging bugs among the teams and having all engineers take a ownership of how the app is working. Swiss cheese model. When I worked at the place with assert_no_n_plus_ones it was the closest thing to that ideal organization.