True, but discussing these questions could help us discover opportunities for improvement. Discourse offers some additional features compared to FluxBB, which may enable ideas for the category structure that simply weren’t possible before.
From the discussion in other threads, it looks like we might end up with top-level country categories after all (which would indeed mirror the structure of forum.osm.org), but I feel most of the forum’s topic-based categories could be replaced with tags on Discourse. There’s no point in recreating “Carnaval kaart” as a category, to use one particularly obvious example, even though we might import the threads from that category as part of the migration.
That being said, you are making a good point in general and we should avoid reinventing the wheel needlessly. When in doubt, we can and should fall back onto the existing structures, and that probably includes the question where to put general/off-topic discussions.