The choice of programming language isn’t that important insomuch as Computer Science is not about coding.
Surely using Python to code OS course assignments does not make much sense. But that choice comes naturally with the course in question. Courses about a specific language are set out to become dated from the start.
Sid is not a rolling release. This is a common misconception.
In preparation for a new stable release, it goes through what is effectively a package freeze. Maintainers are discouraged from updating packages in Sid in order to focus on the new release. So almost no new updates are uploaded to the repositories until Stable is finally out.