It really depends on the topic.

I'm really into a niche of a niche subgenre of books. The Reddit community is the best place to find out about new books and hear people talking about them to get a sense if it's worth your time to read. I used to spend ~5-10 minutes there every day or two to find out about new books.

There just aren't enough Lemmy users into my favourite sub-subgenre in total, and what really made the Reddit community special was author engagement, which will only happen with thousands of active users. I could put a lot of work into making it, but it's just not likely to go anywhere and, without authors, won't be very good anyway.

Hell, even the Parenting community on Beehaw is barely alive, and that's a huge topic that like a quarter of the population might be interested in, and Beehaw is one of the biggest Lemmy instances.

So... maybe? For mainstream topics, sure, but niche subreddits needed a unique intersection of conditions to thrive, which Lemmy can't (yet) replicate.