Tagging content makes more sense than mandating communities. Let 50 similar communities exist but allow users to tag content from a list of defined tags

Users propose tag names and definitions, community votes to pick which tag is “official” when competing tags exist as well as the “official” definition, either automated approval when appropriate (overwhelming majority support) or moderator/admin intervention when it gets dicey (50/50 split on a bullshit semantics argument)

Something like that. This is a solved problem that exists on several aggregator websites to help alleviate categorization. This approach also means that users can propose new categorizations for existing content when OPs are lazy and don’t tag content. Then someone posting us politics news can be filtered without filtering the rest of their content regardless of where they post it