Absolutely - that so much of Reddit's niche and success was being a place where people already were. Folks who made memes or wrote articles went to the place where the audience for that content was pre-built and was focused in a predictable way. Folks who had questions or contributions to make went to the largest community they could find, tied to the content they were focused on.

Absolute reader numbers or absolute activity are only indirect metrics, what the community needs is a large-enough dedicated core to keep a sense of culture and continuity alive, a steady flow of new content or topics, and enough incoming members to replace natural attrition. I find that the last two tend to be strongly linked - for a niche-topic community, one of the best sources of content and activity is beginner questions. Experts often don't have a ton to talk about day-to-day, unless some big news or development has happened, in which case the topic is explored until exhausted and then dropped. But have a steady flow of newbies there to ask the experts questions, and that will prompt not just responses for the newbies, but conversations among the experts on the side.