[devmor]

>most big subreddits have proven quite effective at growing and surviving.

That depends on your criteria. If popularity and user engagement are the only important metrics, this is absolutely true.

If however, clarity of purpose and effective moderation are important, I would strongly disagree. From my experience, most big subreddits that used to fulfill a certain niche have devolved into primarily meta-posting and stealth (or not stealth at all) advertisement.

Of the exceptions to the above, many now just fill the exact same purpose. There are around 10 extremely large subreddits that regularly make the front page that are essentially just "look at this picture of something I have/something I saw" with no real boundary between them.