I disagree. There’s no problem with hundreds of niche communities. They create the opportunity for a real community to form simply by people subscribing to them. And if nobody posts on them, they are still there, not hurting anyone. But if someone does post on them, then everyone who is subscribed to that muni can see that post. So the worst case scenario is basically neutral, and the best case scenario is people have some posts in their feed for their niche interest.