Communities aren't the same as subreddits, Lemmy communities are more like hashtags for an instance. Hexbear is an example of a leftist instance, and the Hexbear Games community is basically a Games hashtag. Trying to centralize communities on one instance is a bad plan IMO because that gives far more power to any given instance.

Community repitition isn't a bad thing, it's an advantage.

If Lemmy doesn’t solve its core issues I don’t expect it to last long and will move elsewhere sooner than later.

you're absolutely right however those "core issues" are intrinsic qualities that come from the fediverse's tankie roots and they're intend to shed power tripping & bad faith users by design.

those qualities like the "fragmentation" keep the discourse going despite the inevitable power tripping mod/admin. the fediverse effectively makes blocking/banning/defederation pointless because doing so only serves to exclude yourself from the main group chat that everybody else can see.

that "sea of inactive duplicates" is probably the biggest outward sign of the intrinsic qualities that serve to sustain its intended tankie users and repels everyone else. if you embrace the fediverse using it's tankie roots on lemmy, you get a wealth of content from niche communities on an entire spectrum of activity levels like the bustling and relatively large star trek communities with the comunist-socialist/doomer-humor/genz-trans perspective on hexbear; or star trek communities with the sarcasm-mandatory/american-political-commentary/propaganda-speak/anarcho-communist perspective on lemmygrad; or star trek communities with the center-right-leaning/moderate/capitalist perspectives from the reddit fueled instances like .world onward all the way to the other end of that activity level spectrum to even deeper niche communities that you could also learn about for yourself if it weren't for banning/block/defederating.

the relatively large user increase from the reddit diaspora has effectively turned the lemmyverse into a digital version of an american center-right mainstrain group gentrifying a tankie digital lemmy neighborhood whose plumbing was built to ensure that no one person/group from the entirety of the leftists spectrum can control/dominate the discourse and that plumbing is going to do it's job and push away the self sorted and mostly inactive liberal echo chamber users.

it's all effectively like digital anti-homeless architecture (eg builtin spikes and split public benches); but with a focus on users who try to power trip when solely permitting nothing but rigidly moderate perspectives through banning/blocking/defederation and only the people too unpleasantly rigid in their world views will be the ones to move on elsewhere; but only to discover that no reddit diaspora has ever survived and they'll end up going back to reddit or sign up for future enshitification with bluesky; where they will do this diaspora thing all over again in the future.

in the long run, the most fortunate thing about this diaspora was that the massive userbase bump was as big as it could be and the political makeup as well suited as possible compared to the other previous reddit diasporas; this effectively guarantees that everyone that could be here to enjoy these leftists safe spaces is already here now and also gives the feddiverse the best likeliest chance for any reddit diaspora to survive.

i once felt the same way about the lemmyverse you do and when i first joined as a reddit refugee. i spent most of my time on .world and the inactive diet reddit clones. eventually .world started defederating at first with hexbear and later with lemmygrad; the controversy peaked my curiosity due to the virulently and almost irrationally strong opinions from the reddit refugees and reading about it has begun to show me how propagandized i am as an american despite thinking that i wasn't as a leftist.

like martin luther king jr wrote about in Letter from Birmingham Jail: moderates have a shallow understanding and the information contained in those instances & known by its users that moderate users ban/block/defedrate from on lemmy have lots of information that edifies that shallow understanding. the moderate users' collective desire to maintain that shallow understanding is going to drive them away from lemmy and these leftists safe spaces are now as fortified as possible to keep chugging along ready to accept future bluesky refugees during their own future enshittification induced diasporas.

Can't you just spin up your own instance and mod/defederate the way you want it to be?

Distributing power across a group of communities over the same topic (e.g. like seats in a congress/parliament) is a nice thought.

However, my second thought was how vulnerable that is in a fediverse. To continue the analogy, an adversary could create new states (server/communities) of arbitrary population (accounts) at will.