I think the feedback from these students and your elegant assessment above is a good insight into some of the challenges with presenting such powerful software to new users.
What about if when you first open darktable, a modal dialog pops up and asks “Need help getting started?” and if you click on it, it takes you to a webpage of high-quality videos that walk you through an example photo of a variety of types (e.g. portrait, landscape, macro, etc) using the scene-referred workflow. As you said, you’d need to be careful to keep the number of these videos manageable, but I think almost every new user probably has a photo in mind that they want to try processing when they try out the software, so letting them find the example video that is most similar to their photo, then watching it, and then repeating the steps on their photo will help get them started. Of course these results won’t be optimal, but it would at least let new users successfully process a photo without needing to deep-dive into the documentation until they feel confident in the basic workflow