I think there is one main difference between xmpp and activitypub. A chat protocol gets better the more users it has. So the users were the killer app. xmpp arguably wasn’t much worse off after Google left than before it got there.
Mastodon is a bit like this, in that lots of users are probably looking for the same type of content from the same users as they got on Twitter.
kbin/lemmy are a lot less like that. I just need enough people to surface interesting content and have a meaningful conversation. And I’ve already (mostly) got that now. If meta brought all of their users to link sharing it would probably get worse with clout-chasing, organic marketing, and low effort crap.
It’s grim. Obviously twitter still holds sway over a lot of people. And spreading malinformed propaganda is bad.
But it really underlines that anyone with any conscience whatsoever needs to disengage from it. It’s not okay for governments to engage with it. And though I don’t suggest that capital cares has any sort of conscience, but engaging with it has been increasing in cost and decreasing in benefit. NPR recently left, for example, and saw nearly no impact whatsoever. So the cost of leaving is low.
Ideally people would deny it any money, advertising or otherwise, until it ceases functioning. I suspect Musk will continue to be a delusional asshole for years to come. But at least twitter will be dead and gone.