This isn't how any of this works at all. Defederation does not increase your privacy from them. That's not how federation works. They still will see your posts. Blocked or defederated. You just won't see theirs. Blocked means you filter out their content. But they could theoretically show up in comments. Defederated means it won't populate. But it doesn't mean your content won't get populated there. They simply can't comment on content from or direct message folks on a server that defederated them.

Privacy through obscurity is as bad as security through obscurity.

Any real danger Meta presents is looming regardless of federation. I'm not against defederation. I'm just against defederating without purpose. And to be honest, what I've heard so far leads me to believe defederation will be my likely call if and when Threads goes live with ActivityPub (well, defederate with their primary instances at least, not sure of the details of how one can defederate with every Threads based instance, though it may be simple). But I don't even know if they'll federate with Lemmy/Kbin to begin with and I do not want to start some trend of instances needing to act on hypotheticals.

Tl;Dr - defederation does not increase your privacy at all. Not saying you shouldn't defederate for other reasons, but your exposure is absolutely unchanged one way or the other. This article has federation entirely wrong.