Nope not at all, this is where the misconception is.
Defederating works kind of like a one way block, you stop your instance (Server A) from being able to see content from the other (Server B)
Server A can no longer see any content from B
B can still all the content from A, however users of B can no longer comment, upvote, downvote etc the only thing they can do is read the content of A
This is the same for Lemmy, Kbin and Mastodon
Defederating is for when you don’t want your users to see harmful content (bots, extreme ideologies, problematic posts etc), if you just don’t want to see the posts then fair enough that’s the way to do it
If you care about the privacy aspect of Meta seeing your comments/posts or about not wanting Meta users to see your content then no, defederating won’t achieve anything