This is a wrong and surface-level reading of the original post. If there are "cases" in a system, then there are going to be "edge-cases" as well. The problem is in classifying certain cases as "edge" and others as regular. We do this because the regular cases are very obvious and are either the perfect happy-path, or a failure condition that we would immediately consider.

But between these two exist a permutation of conditions that exists in the domain and often manifest in production. Either we can actively manage them thanks to types, or we can let it end up in production with hard-to-track bugs.