Im joining in on the reddit ditching thing, and was kinda worried at first that i wouldnt be able to like use it the way i did reddit as it feels like a whole new place, but after engaging with posts and people and actually being a part of lemmy rather than being lurk mode all the time i was pleasantly surprised with how easy it is to become a member of the community, theres a reasonable amount of subs (or whatever the other word for em is) that fit my interests, enough linux content and shitposting for my liking, and the overall random posts made by people equally fed up with Leddit. (also i admit i used reddit a little cus there was this post on the fedora sub showing how to fix a sound issue i been having after a recent update)
Some instances might just focus on a topic. And I agree that makes sense.
On Reddit all the subs are community run too. So if two subs merge or redirect or something that is just because the mods of that one sub decided to do so. It’s not like reddit is forcing anyone or making those decision. Nothing stops you from creating r/askreddit2 and decide to not merge it with the “main” askreddit.
The same thing is possible here. And give it some time. At some point I hope that certain communities for a topic will establish themselves with good rules and good moderation over others and then there will a natural flow towards those well established communities and there will be less overlap. It really is exactly the same situation here as it is on reddit.