Currently you are correct. I am subscribed to multiple technology communities and they show up in my feed with all my other subscriptions. I often get cross-posts in multiple communities. Since I browsed reddit this way it is not a huge change for me, even the cross-posts.
Lemmy is new and still under rapid development. This mass migration came at a good time to boost user testing but maybe not the best time to accommodate a complete exit from reddit.
There are efforts to figure out a way to join multiple communities, but I don't think a method has been decided yet. Some suggestions are:
- user multi-reddit style groupings
- auto grouping communities with the same name
- moderator curated grouping
- post syndication between communities
The distributed nature of the Fediverse is its power and weakness. It makes it hard to kill, but also hard to join together.
Keep posting and giving constructive criticism. It will get better.