Given the fediverse is pretty open by design, meta doesn’t even need to be part of it to spy if they wanted.
They can’t gather all the same information that they could from a phone app, and we’ve seen what permissions they ask for on that. They also can’t manipulate the feed to drive engagement by fostering hate like they can with their own site/app.
It’s the EEE strategy that people are more worried about.
Hence the “get them off meta and onto other instances and then defederate” thing.