So I'm part of the reddit influx. However, I've occasionally checked lemmy out a few times over the last few years looking for reddit clones. Lemmy had no real users or content (as compared to the bigger online communities, or even usenet of old). From my brief visits, there wasn't much culture that had been built up yet, and it was mainly open source enthusiasts discussing federation. I think beehaw had been working on a decent community for a while, but they've de-federated with some of the fast growing instances. It would be good to post there and find out their perspective.
I think your question is a really good one though, and I'd love to hear answers, but am also getting a feeling that lemmy is a new space that is just now really taking off into its own with this new growth.