Badly moderated subreddits get replaced all the time by better moderated ones. The system is inherently meritocratic: if you abuse your modding power then your community is going leave and go somewhere else.
If you're talking about the ginormous default subs, then yeah -- the landed gentry analogy is kind of apt. You can't just make your own alternative to r/pics or whatever and expect to gain traction without some unique angle and a lot of work.
(Although, again, this is how open source works as well. You can't just fork Debian or ffmpeg or Rails and expect a community on Day 1...)
If you're talking about the "long tail" of smaller subs, those get forked/replaced all of the time if there are mod issues or if somebody just has an idea to cover a specific topic from a different angle.
For an example, a lot of people didn't like the moderation tactics of r/audiophile, nor their refusal to look at affordable gear, so some of us made r/budgetaudiophile. We serve different parts of the audience and we cooperate with eachother. And both of us refer headphone-related questions to r/headphones. That is an example of things actually working Extremely Well.
Reddit is in an interesting position. I think its only real value is that long tail. That is where the actual valuable content+community is. The ginormous generalist subs get huge traffic but are utterly disposable - there's no real reason to get your memes or whatever from Reddit vs ICanHazCheezeburger vs random meme-based Facebook group etc etc etc etc etc.
Subreddits may be nearly infinite, but good, descriptive subreddit names are not. r/videos is going to get more natural traffic than r/ReallyCoolNewVideos, which is going to get more natural traffic than r/asdlkajflaksjf.
Sure, but it's a reddit joke, because r/trees is devoted to marijuana(which exists because of a protest against bad mods on r/marijuana).
Probably non-reddit folk will be turned off by the name, and not get the joke. And I bet a lot of members of that sub only subscribed because they are inveterate redditors and not because they're interested in the subject.
r/videos gets more natural traffic because it's a default sub. Regardless, making a subreddit isn't some competition. You don't need to be bigger than the subreddit you're forking from.