A complicating factor is that teams usually start with E2E when it’s simple, and only move to other approaches when the systems have become way too complicated.

A complicating factor is that teams usually start with E2E when it’s simple, and only move to other approaches when the systems have become way too complicated. At that point I don’t know if there is any specific strategy that effectively catches a lot of bugs, short of sending to production and monitor the effect. At a company we just called those tests “sanity checks”, and the goal was just to make sure the most basic use cases would still work, and nothing more.