I have a feeling that many of the people who moved here are the most active ones who also probably used a 3rd party app. This has two effects: Lemmy becomes much more active despite the relatively low amount of users while reddit loses many of its most active members while keeping the lurkers that don't contribute and thus the content quality is going to see a significant drop despite the amount of users remaining about the same.

Lemmy doesn't need hundreds of millions of users to become better platform than reddit. We just need the most active ones. Facebook still exists too and is succeful on paper but who even goes there except my parents? For all I know that place could dissapear tomorrow and I wouldn't notice. It effectively doesn't exist to me already.