The biggest problem I see is fragmentation, people are creating the same community in different instaces, /c/Piracy for example.

I agree, to an extent. You're right in that if you were part of the vibrant community of /r/piracy then it's miserable to see it shatter here on lemmy. That said, this only applies if you're expecting lemmy to be a 1 for 1 reddit replacement. For this type of community to remain cohesive, /r/piracy would have had to spin up their own instance and in /r/piracy direct everyone to lemmy.piracyinstance.whatever.

You can't really "fix" this in a central way because even if you did, it would be trivial to create an instance that would allow duplicate community names. Also, I can see a lot of use cases for lemmy which do not intend to be federated.

That said, it's not necessarily as big a problem as it appears, if you just accept that this is how the fediverse works. There's no single source of control, so of course people can create 147 different /c/piracy communities if they wish to. Once you accept that, then it's not really that difficult to subscribe to all the /c/piracy communities you can find.

The problem itself could be diminished by a few new features which I feel certain will emerge in the future:

• linked communities, where one communities content is syndicated to another. So if you post in !selfhosted@lemmy.world then you also post in !selfhosted@lemmy.ml. This would work differently to cross-posting, all comments would be reflected on both instances.
• grouped communities, where you can subscribe to a group of /c/selfhosted communities with one click, so you see them all in your feed.