I think if you had one you’d likely know, but you can flip your /latest list into activity order to double-check using the column title or using YourSite/latest?order=posts.
But something like this in the data explorer should also show you the top 10:
SELECT id AS topic_id
FROM topics
ORDER BY posts_count DESC
LIMIT 10
The SQL for the Reader badge is here:
The Reader badge isn’t necessarily one of the most exciting ones, so if you can live with disabling it and that fixes everything that might be the easy way out. But if you want to explore it further I think you may want to look at your post_timings table to see how big it’s gotten.