This set of really good questions by @jjosephmiller gets at the heart of what the CMS’s job is. Do its “content types” (or templates, or post types, or entity types, etc) necessarily map to the conceptual “kinds of content” that exist in the high level map of an org’s content?
I tend to think that the content types defined in the CMS are more like the “physical model” in database terms — they represent how the conceptual model of the content that is agreed upon by the org and its various teams gets implemented within a given system’s constraints.
Sometimes the difference between two conceptual content types (like the ‘report’ and ‘working paper’ examples mentioned in the original thread) is taxonomical rather than structural. Whether it’s an “A” or a “B” is useful information but doesn’t change how it’s created or used.
But just as often there are significant differences beyond simple structure — divergent workflows for the two kinds of things, different destinations in a web site or various output channels, different authoring permissions or UX affordances during creation etc.
Some CMSs treat “content type” as the official hook to hang those differences on, and breaking it down any other way introduces quite a bit of complexity. In addition, editors often think of A and B as very distinct things, even if both are a single content type under the hood.