That doesn't work, though. If I add posts and comments to, let's say, a Brazilian Jiu-jitsu community on Lemmy, that's just one more number. That isn't going to improve.

Reddit had a huge boost from Digg, and even then, it was a different time when fewer numbers were fine, and people were more willing to engage in social media at lower numbers.

If Lemmy instances are to grow, that engagement needs to be directed. It needs popular communities to be highlighted, and once consistent interaction is there, growing communities need instance owners to direct traffic/engagement their way. That's how subs like /r/soccer got off the ground, and it's probably the only way it'll happen on Lemmy.