If we are to persist in the sub-sections (sub-topics / sub-categories) - how about the following:
For any Main Topic, (where sub-topics exist) then clicking on the Main Topic will show all questions in all sub-topics in the usual date order.
However, you can not post a new question to that Main Topic, and must select a relevant Sub-Topic in which to post your question.
That way, (and where they exist), we all use the Sub-Topics, yet if we just want to browse the latest questions in the Main Topic as a whole, we can do, without having to go through each sub-topic individually.
Does that make sense, or am I rambling again??