But you can accomplish the same thing by creating new more moderated subs. That's why we have /r/AskHistorians in addition to /r/history. If the sub isn't specific enough the solution shouldn't be to falsly and silently fragment the sub's users via user-side filtering, it's to explicitly split off a different community that behaves the way you want. In that way there is no "non too specific sub".

If you participate in a subreddit, but filter out 70% of the content, in what way are you participating?