I think people will flock to wherever there's activity. Then my random series of thoughts:

Firstly, there's some rumblings about setting up some kind of multi-community feature (either server-side at the community level or client-side at the user-interface level), so hopefully this comes around sooner rather than later.

Secondly, Lemmy does support cross-posting formally (for example, if you submit an identical link to multiple communities, there will be a small bit of additional text indicating it has been cross-posted and linking out to submissions elsewhere), but text-based cross-posts are not as technically featured (this might have changed, but when I last tried it merely appended a "crossposted from XYZLINK" to the start of the text body).

If a critical mass of people congregate, they may want the episode-posting bot to work on their community anyway.

The broader pragmatic perspective is it's pretty evident there are a number of people interested in participating around anime and manga centric topics, but the fact that people are spread out across a variety of different communities makes it difficult to reach a critical mass for conversations to start self-sustaining themselves. If you and like-minded individuals are interested in committing the energy and effort to grow something, I'm definitely happy to come along and help out. Ultimately though, the addition or removal of automated episode-posting bots doesn't really change the fact that it's hard for incidental participants to stay engaged if there's little conversation about the episodes or anime in general, and from my PoV the real "content" are in these discussions rather than in the submissions made. In some ways, a lot of these individual episode threads become mini-communities in and of themselves.

There is absolutely nothing wrong with starting something and then handing it off to someone else later either.

I mostly participated in episode discussions on r/, but I feel I did benefit from other threads there, e.g. hearing news about new shows, getting linked to new official PV / posters, etc. I don't think you need to restrict it to episode discussions only, but do it as you like.

One thing I think the mods there did right was limiting random chit-chat overall by keeping them in the weekly chat threads so the sub feels mostly on-topic and not too chaotic.