This. Some of the users in my favorite niche communities have migrated over, but overall, it's still a bit of a ghost town compared to the same niches on Reddit.
Reddit was at its best when you stuck to the smaller subs where people were primarily positive and cheering on newbies, which really makes for active, welcoming communities that I truly miss. Having a bigger user base in those smaller communities is invaluable, because having a place to come and get advice from people who've been around the block is way different than the blank canvas you find in the same communities on Lemmy. My personal favorites were subs that specialized in "you like this? Have you tried that?"-type threads, and one of the coolest community norms I ever saw was in r/doommetal, where instead of blacklisting bands that got posted too often, they had the "Green List," and anyone who posted anything from the Green List was cheered on and inundated by suggestions for more bands similar to the OP.
I found many of my favorite small bands and content creators in subs like r/doommetal, r/OSR, and r/boardgames, and the amount of good advice I got in subs like r/professors, r/luthier, and r/chempros is impossible to overstate.
I'll miss my reddit niches, and I just hope the Lemmy niches eventually grow up to be a real replacement for those communities.