I would say the edge cases
What you call "edge cases" is all that I'm seeing. I don't browse by all and I don't go around chasing communities which I know I won't like. I find all the popular ones (news, technology, meme ones, etc) boring beyond belief.
situations like the language one can be implement with a UI fix.
There is already a "UI fix", which is to let people to determine which languages they accept. Thing is, most people don't use it.
The "browse by all" is a similar situation. The system was not designed for it. It's just because the Lemmy network is still too small that people are still using it like that. As soon as the network grows, most people will hopefully realize that it will be impossible to follow the firehose on any instance that is reasonably federated.
I think our misunderstanding is not about the values, it's just a matter of perspective. If you value the same type of content / interaction that of the average Redditor, then you will want different things from those that used to like Reddit because of its niche communities.
It is supposed to, but it isn't working. Niche communities are still outnumbered by posts from more active ones and people in the larger instances see content from smaller communities and use the voting system like they are training some algorithm.