A potential federation with Threads (should Thread decide to implement it) would overwhelm Lemmy/Mbin/Piefed with millions of users (compared to the 40k monthly current active users), transforming those platforms into a threaded version of Facebook
No, .world is not anything like a 'main page'. It's just the largest "instance".
Lemmy isn't even really a site, it's more like what email is - a data exchange protocol.
You see mostly .world content because you share that domain, and they've "blocked" a lot of other domains.
You can make an account at any-other instance and see a lot of other content. Lemmy.world has "blocked" (defederated) with a lot of instances, so you're not seeing everything.
Sync is just an app that lets you view your account content (similar to how gmail the app lets you view your email content).
There is no "main page", different instances host different communities and users, but everything is still connected by default (sometimes instance disagree and prefer to block each other)
So if lemmy.world has defederated with many other instances, would that mean that clicking 'All' in the example provided won't show content from those instances if your account comes from lemmy.world?
Yes. You will not see content from an instance that has defederated your home instance or that your home instance has taken action and defederated from.
It's the biggest instance, and the one you signed* up at, so in essence, for you it is. However the content you see there will be made up of not only users and communities from Lemmy.world but also from all the instance they're federated with. I'm registered elsewhere but you'll still get this reply.
I'm a .world user just because it had a lot of users when I signed up, but I've seen some hate thrown at it recently. Is there a legit reason I should consider switching to another instance, or is it just hyperbole? If I did, would I be able to migrate my account and its post/comment history (not that I really have much of a history at all, I just lurk mainly) or would that be stuck on .world forever?
This post gives a summary of the issues people have with overcentralization of users and communities on LW: https://lemmy.world/post/14728407
This is a meme but with some technical explanations why instances like aussie.zone have a 7-days delay with LW, but are up-to-date with all the other instances: https://lemmy.world/post/20575394
You are able to export your subscriptions and block lists to a new account using your settings (there is an export/import function). You cannot import your posts and comments, but if you use the same username and add your old account in your bio you can still show your past posts that way.
Your comments and post history cannot be transfered presently. If you're already there (and fine with Threads potentially appearing) then its fine to stay. Too many communities are hosted there though so if you intend on creating any it would help the user base if you made it elsewhere.
Lemmy.world is one of many lemmy instances. Any Lemmy instance will show posts on their “all” page from instances they’re federated with. Generally, you can subscribe to and comment in federated communities.
Depending on your viewer/app, you’ll see the instance following an @ sign. For example, username [email protected] means that account is on the sh.itjust.works instance. Similar for communities.
May have missed some finer points but that’s generally how it works.
There was only ever one "main lemmy" instance, back in the days when Lemmy.ml was presented as the official flagship instance on the official lemmy project page by the official developers. And was the biggest instance that absolutely dominated the lemmyverse.