Oh no, a new discussion board is neither as robust nor as polished as one with over a decade of use and revision.
Most of the complaints are just whining that Lemmy isn't a perfect drop-in replacement for his love of endless, constant time wasting on Reddit. OTOH, the issue of multiple, nominally identical communities on Lemmy is a true weakness of the platform (imho, of course).
The multiple communities doesn't bother me, I just join both and usually don't notice the difference. It's a better problem than all the communities being on lemmy.world which defeats the point of federation.
My issue is that it's an inefficient use of human resources because it clutters the interface. If you're looking for the answer to a question, you have to post in multiple places and/or search/review multiple communities to see if the question has already been answered. For low-traffic communities the replies get split, suppressing topic participation. For high traffic communities, stories/links that get posted to the "same" community on multiple instances clog up personal home pages and - in the case of large participation - clog up the top feed.
Again, imho, there should be a way for communities to aggregate or sync across instances and be shown as a single feed, like a symlink to multiple folders that is treated as a single location for end users. I realize this causes moderation concerns. I still think its better for the participants.
One person posting the same thing to multiple communities is bad etiquette, whether the stated purpose of those communities is the same or not. Anyone who does this should be shamed, blocked and banned. Find the biggest and most relevant community and post it there, don't spam.
I focus on comments rather than posts, but if you care about finding new links then I agree that duplicate communities is a problem. But it's not the biggest problem on the platform, and obviously while instances are independent there's no way to force a solution. Communities have merged, but it's usually small communities on small instances dying as their users move to a large community on a large instances. This is a disaster for decentralization, everything needs to be as spread out as possible across instances.