In regards to Kagi News, there is quite a bit of content repetition between categories, often. This is something that should be improved upon.
Repetition of the news articles between categories can be eliminated by utilising "categories selected" and can by using "sources" to trim the repetition of news for a user under different categories. There are already hierarchies existing for this in the repository (Core feed and Kite feeds), and this can be used for mitigating repetitions.
Elimination of these repetitions between categories will greatly help the content delivery and reduce the bloat.
For example : If a person is subscribed to both World News and UK, there is no need to show the news shown in the category "World" to repeat and be shown in the category "UK".
If category "World News" shows the news, then the sub category (here "UK" ) should eliminate the news shown in the main category. This might get the sub-categories thinner in content (if subscribed to both primary category and secondary category), but it will keep the news reading experience cleaner.
There is no need to remove content if a person is subscribed to just one non-overlapping category (either from Core feed or Kite Feed). Imagine if multiple categories are subscribed, the repetition compounds and bloats the feed. This also makes the app feel vapid in content delivery.
Ground News has some good category based delivery, but even they have some bits of overlapping news, sometimes.
A toggleable feature will be an over engineered solution to eliminate repetitions, but just category-based overlap elimiation of content by default will be the best approach for this issue.