Entities define the attributes that make up a piece of content. Rhetoric is about the actual data contained inside those attributes.
An example might help.
Consider a bicycle and an e-scooter. They are made up of very different components—one has a seat and pedals and the other has an electric motor and a charging port. But in most cities, the two have the same function: helping people commute (relatively) short distances more quickly than they could on foot.
An e-scooter’s technical schematics are an entity.
Users rent an e-scooter for its rhetorical function.
If you’re a company in the business of renting out transportation modes, it certainly matters a lot whether you specialize in bicycles or e-scooters. Having the right set of technical schematics definitely matters to the people who build the devices you’ll be renting.
Commuters don’t care which thing you make, so long as they can find one of them right outside their door when they’re running late for work.
And, as I discussed elsewhere, items with different sets of attributes can have identical rhetorical functions.
Think tank content isn’t like a recipe. It's full of editorial content, of narrative text whose internal structure can vary from one item to the next. It is content whose rhetorical functions can vary.
For an author or editor, content type refers to the rhetorical function a particular piece plays. A working paper, for example, is intended for other researchers, is not meant to be the author’s final considered view on a topic, is not usually peer reviewed, and doesn’t weigh heavily on tenure decisions. By contrast, a brief may be written for a high-level elected official, provide just enough argument to demonstrate its seriousness, and leave out most of the mathematics and detailed charts.