One of my largest pain points with Lemmy is that there are multiple active communities for the same topic, causing quite a few duplicate posts to show up in my feed that is difficult to filter. Hopefully there comes some kind of solution, outside of userbase, this is (what I believe) one of the larger issues compared to Reddit.
However, I still switched over to Lemmy for my primary 'Reddit'-needs.
Lemmy does not offer that, unless you are using an app that does it (I don't know which ones).
PieFed though just added user customizable "Feeds" that allow you to join together whatever communities you want, and then share that collection with everyone. Recent discussion about it.
There isn't an official app for PieFed (although API testing is underway using Thunder, and iirc Interstellar also wants to add support for it), so it's just accessed through a web browser.
It helps to see communities as categories for an instance, each instance will have a different response to the same post based on the general instance vibe and culture. That's also why picking a good instance to browse locally can be pretty useful.
I like that view, and it made me think of a possible "implementation"/"fix" as well:
Combine the post somehow (Based on attachment/title/something else?)
Filter/categorize the comments by instance that the comment was originally posted towards (Not by user, as that would be awful)
The largest issue here that I can see, how do we treat "new" comments to a post?
My annoyance is primarily with the fact that I see the same image 3x in a row, on a fairly regular basis. I might unsub from a few communities that share the same content.
There are many different workarounds, I personally don't put much stock into sorting by "all" generally, sorting locally tends to be a better experience and has less repetition.
You can pseudo-curate by only subscribing to your most prefered instance of comm, but you won't be able to see instances with allow-lists as the basis, rather than block-lists.