> Any moments of "lightning-in-a-bottle" can certainly result in memorable periods where a subreddit truly adds value to one's life, and that can make the whole website hard to give up.

I would mention /r/credibledefense as a counter example. It was a niche subreddit before the Russian invasion of Ukraine, in the aftermath got popular, but still managed to keep its quality.

But I agree with your general point, it's not a huge problem for me, though. Some subreddits get popular and thus bad, some new subreddits get created. Reddit's relative anarchy is its saving grace, communities can split/fork, but still stay within reddit platform.