Intermediate lessons are much shorter, because they tend to focus on smaller subjects, whereas the rapid developer courses try to cover all the basics and are therefore much broader in terms of topics. So yes, they are indeed pre-intermediate.
The Rapid Developer course is for non-technical people or people with little or no programming experience, knowledge or skills. It is designed to introduce basics functions of Mendix with hands-on practice in building an app with Pages, Domain Model, Microflows, Nanoflows and Security.
The Rapid course is designed to prepare people for the Rapid Certification exam so it is a longer course (16-24 hours) as it covers a lot of material/features and provides context and explanatory information for the features and functions of Mendix.
The intermediate learning paths are designed for people who already have foundational knowledge of Mendix and experience developing apps so those paths are shorter as some assumptions about what the learner knows and can do are made. Plus there is an expectation that the learner knows how to find solutions in Forum and Documentation if the learning path is not explicit enough to cover all the details of the feature or function presented.