I really like how you phrase this and completely agree. Issues should be caught as early as possible in the dev process and what you describe is probably as good as it gets. I tend to look at such problems from an organizational perspective and a good APM is a fail safe that compensates for other failures.

> 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.