That version had been forked far enough away from upstream Lemmy to make federation impossible, so we were our own site for a couple(?) of years

It's worth noting Lemmy was pretty rough back then and the reason it was forked was because a lot of features we really needed for a forum of this size didn't exist yet, it didn't have anything to do with federation (not saying you suggested that, I just thought that's a misunderstanding which could be read into your comment)

I don't think its known how much of the userbase were originally /r/chapotraphouse users and how many have joined since the Reddit ban. I would venture a guess that at least a significant plurality of the people here are probably from the subreddit and either came here directly from the lifeboat discord or were former /r/chapotraphouse posters/lurkers who eventually found Hexbear in the wild.

I would be surprised if it wasn't still a majority. Federation has brought a slow trickle of users, and a very tiny number of users have come from word of mouth from existing users, but /r/cth was enormous and it would take a lot of attention to beat the userbase we started with. The entire reason /r/cth got quarantined and then banned was because it was such a big and active sub that there was communist propaganda hitting the front page of Reddit constantly and they couldn't do anything about it.