IDK, it seems that once a community gets big enough, it devolves into an echo chamber so the unique perspectives get drowned out. Sometimes the unique perspectives wins and slowly propagates through the community, and sometimes the unique perspective gets buried, but uniqueness is rarely highlighted.

For example, I used to be active in /r/personalfinance (kind of a cesspool imo), and there have been times when my perspective won out and I saw it get parroted (often incorrectly), and I was later corrected by yet another perspective and that one got buried and to this day people are parotting my incomplete perspective instead of the more correct perspective. I tried correcting it, but ended up giving up.

So a community needs to be big enough to have diversity, but not so big that the hive mind takes over. I think that magic number is somewhere around 10-100k people.