I agree that small communities are better, by the way, the way you talked about is mostly how it is in language learning servers, some are really comfy, even more if its of a single language only and one that isn’t usually listed as most spoken languages worldwide since people learning those others have very really specific curiosity/need/couldn’t find many communities on it. Maybe you’d like it more, I don’t know if there are Matrix servers like those yet, maybe I just haven’t found too.
When it comes to Discord, I think it’s easier to sign up on Matrix than Discord though, Element is pretty straightforward and already pre-selects an instance when signing up for those who isn’t familiar with decentralized tech yet. I bet if Lemmy had a landing page for people to share when trying to convince others to join to sign up and pre-select lemmy.ml (since it is maintained by one of the devs, you are already trusting using their software anyway) it could help, or not, just an idea.
I have managed to get friends to use Matrix but not switch, if they don’t even bother to try using it (i really mean use, not replace or switch, that’s a bigger ask) they are either just lazy (I don’t mean it in a bad way, some people usually are because they are in a bad mental state and just too exhausted day-to-day) or it’s just not worth your time as much as you think. There are friends and there are people who are just going along.
Have you heard of Neocities? They’re also open-source.