I agree, but I think we need to be a little more granular than this. We don’t need to create a 1:1 mapping for every subreddit, but if at least we can make it in a way that each subreddit has a recommendation in a adjacent sub-category, it will be better than just pointing to the closest/most popular community in the higher-level category.
Imagine if you are into one specific genre of games and subscribed to a bunch of different subreddits through the years for the games you enjoy. When you come to Lemmy, the recommendation is simply that you signup to a generic “Gaming” community, only to find out that no one is really talking much about your niche genre. You’d be more likely to say “this recommendation is non-sense” than “ok, I will start posting content related to the things I am interested about”.