Yep, that all makes sense. To clarify, what I've seen is that users will refuse to populate a site until they're dead sure it's going to be The Next Big Thing and achieve exponential growth, which basically ensures that no new site is going to get to that point except under wildly, improbably favorable circumstances. I was a KS backer for Pillowfort, I tried to get people to give it a chance, and a few people did--but it was like a middle-school dance where everyone was standing around the walls waiting for somebody to get the party started. I think that's a natural human thing--I'm guilty of it, too--but my experience was that there were many clusters of interests with one or two posters who didn't know each other and couldn't bring anyone over, so they felt like they were talking to themselves.
I knew no one on Cohost when I got here except via name recognition, but I felt comfortable posting because there was already a pretty clear sense of Site Vibes. Money aside--which I know only works in the hypothetical--it had gathered enough people talking to each other that those people could probably continue talking indefinitely as a small community. And, critically, it did not matter if they shared much common ground in the form of stuff like fandoms or hobbies or jobs. A lot of the early posts I saw had the sentiment of, "It should be cool to talk to other people here about whatever," because that was what people were looking for.
So the encouraging takeaway is not really about business model or even size, but rather that by cultivating some kind of encouraging/reassuring direction for casual interaction, that's something that users can immediately get invested in rather than thinking, "Well, if everyone doesn't move over there, is there really any point in having an account?"
There's actually some wild parallels here with MMORPGs in World of Warcraft's prime, now that I think about it--a lot of people feeling like they had to pick one game to invest in, and if it wasn't going to kill WoW and take all its users, you might as well play WoW. It wasn't until WoW started naturally declining that people kind of shook out of the idea that a successful MMO had to be that size to succeed, or that smaller games (which are still massive, because MMOs also need to have a ton of users to be profitable) would just burn out and die.