You got me. I think that the approach of having to subscribe to a community on every federated instance means that discovery is kind-of broken. I get that it is 'working as intended' but I think that may have had unintended consequences.
The result has been monolithic communities which are all the 'same', and it ends up splitting interests across communities, which will inevitably slow growth, and prevent lemmy from being a true reddit killer (this is basic math of networks and how they function).
I know the developers are doing their best, but I think at a high level lemmy needs to be reconsidered. Instances should be focusing on some niche thing, like poland ball humor, or skiing, or woodworking, each with niche communities within them. For example "wintersports" might have communtieis for skiing, cross country skiing, maybe one for showing off your new skiis, etc... That way your 'home' is around your central interest. Then allow 'all federation' across all instances (if you want to).
This wouldn't be so much a software change as a cultural change to how we approach making lemmy's (aside from the discovery issue).