I appreciate the effort, but what is happening is option 1, aka merging of communities, naturally.

About knowing where to post, you can usually have a look at https://lemmyverse.net/communities, search the community name, and have a good idea of which one is the most active.

Sometimes different communities can coexist, and that’s fine. !science@mander.xyz and !science@lemmy.world have different audiences, and that’s okay.

There are several case of divides, such as !moviesandtv@lemmy.film and @movies@lemmy.world

I can see the genuine need to post to several communities at once

Liftoff has been doing that for A while

Lemmy.world holding such a prevalent place in the Lemmy/Kbin part of the Fediverse makes it a major single point of failure.

They should still be the newcomers instance, but communities and users should migrate to other instances to increase the resilience of the Fediverse.