It’s blatantly wrong. Google extended XMPP for their own purposes and when participating with XMPP no longer suited them, they left. The collapse of the “XMPP userbase” is a misnomer - those users were never XMPP users. They were Google Chat users. When Google left, XMPP was in the same state it was in before Google got on board. It returned to its status as a niche protocol for a service that, as @effingjoe@kbin.social points out, people didn’t really want anymore.
I don’t think that’s true. Unless it’s a server side server denial rather than defederation, all posts on Lemmy are public. This means Threads will directly receive updates even from defederated instances.