The psychology of this problem is that users are too lazy to maintain multiple accounts when all they have is Lemmy’s stock web client. So they choose one of the big nodes: lemmy.world, sh.itjust.works, lemm.ee, lemmy.ca, etc.
These Cloudflare-centralized nodes are able to greedily exploit the #networkEffect because due to lack of multi-account software. If there were some well-made 3rd party client apps for Lemmy that would be designed for multiple accounts, then more users would be willing to create accounts in more decentralized parts of the fedi.
Mastodon somewhat proves this because the client-side tooling is in place to make it convenient to have 6 or Mastodon accounts. And Mastodon nodes are better balanced.
Every node has a different set of relationships to other nodes. If you create only one account and you choose a small low-activity node, you’re isolated by which nodes are federated and defederated to that node. The front page timeline is also limited by the subscriptions of others on that node which narrows what’s exposed to you. And worse, because most of the population has disregard for decentralization, those subscriptions are mostly to communities on the biggest nodes which exacerbates the imbalance.
It’s good for the decentralization principle to avoid the large nodes¹, but doing that bring isolation and limited exposure. So to counter those problems you need accounts on multiple small nodes.
¹ This means not only avoiding having an account on the large nodes but also avoiding communities hosted on those giant nodes.
Otherwise I don't see that as a problem, it's just like forums with the addition that you don't need an account everywhere. You can participate everywhere. There are also good searches for communities.
I’m quite familiar with relays in the SMTP context which is not a context where an end user installs relays. An end user in that case would only direct their own software to use a relay that has been installed by a service provider in control of a server. So when you say install a Lemmy relay, I’m missing the concept. What exactly is a Lemmy relay? Can you walk me through this scenario: suppose someone is on Beehaw and they cannot reach node X because Beehaw defederated from node X. What are the steps for a Beehaw user to subscribe to a community that is hosted on node X?
If the instance has blocked another instance, then the user cannot do anything except change the instance, as his interests and those of the operator probably do not match.
A relay in fediverse is a server that receives messages from the instances connected to it and forwards them to all connected instances.