Lemmy

Not really. Even in worst case scenario (everyone migrates to a single instance), lemmy.ml is considerably wider in scope and userbase than the socially rejected in Voat.

You also have a difference in circumstances. People aren't moving to lemmy.ml because they think that Reddit's moderation and rules are too restrictive, unlike with Voat, which would change who is actually moving over, and the community through that, which is probably why Lemmy's community is a bit on the tech-inclined side, and is a bit less of a politics quagmire.

If federation is disabled by default (is it?), I think that this might have to do with spam and bot prevention. I’m not sure however.

Not to my knowledge. It's probably just a case of it not existing on their instance, but coming up as disabled on their app. Trying to load it up, even on lemmy.ml, seems to just return a "community not found" error, which means that there just isn't one made with that name, rather than a community existing, and being disabled.

decontextualisation - ipsis ungulis “Then read it locally with libreddit”, letting the reader to guess what you’re referring to. (I got it, but someone else 2m later won’t).

Can confirm, was a bit confused. But even with context, 2 TB of data is a ludicrous amount to expect someone to pull. At an optimistic household connection speed of 50 Mbps, that's 4 days straight of uninterrupted downloading, and a lot of off-the-shelf consumer devices don't have that kind of capacity to spare. It's retro, but not in a good way.

That's also a Reddit archive, and would be limited in what kind of posts that it would contain, as anything made after the archive snapshot was taken would not be in it.