From my experience, programming and technology communities are already really strong on Lemmy. I'm confident to say that if you care about these topics, moving from Reddit to Lemmy is a good option.
For another categories, they're still small and having struggles gaining traction to have enough users and posts to be lively. But I think it's just a matter of time if Lemmy continues polishing its features and community discoveries.
Lemmy has been great for me. It took me about a week of scrolling through Lemmy's r/all equivalent to find enough interesting communities to sub and filtering out the rest. Now both my subscribed feed and all feeds are generally high quality and aligned with my interests. It does feel like they're growing.
It’s really only lacking the size of Reddit for me, there isn’t a ton of activity in niche subs, but they’re growing.